A much improved aspect of Diablo II, quests are now more immersive, complex, and inventive.  There will be around half a dozen quests per Act, with one main "Defeat the big boss" sort of quest (Andariel in Act One is the only one thus far confirmed.) per act, and a number of other sub quests.   Some quests, the so called "guaranteed" quests, will be in every game, while others appear randomly.

Most quests are a bit more involved than the "kill a unique monster" type of quests in Diablo.  You must now retrieve an item, or clear out a portion of a level, or else complete one quest in order to be given the next quest by some NPC.  While the main quest in each act (defeating the big boss monster) must be completed, some of the sub-quests are optional, though you will mostly likely need to complete them all at least the first time you play the game, as they will provide you with items, experience, and knowledge that your growing character will need to complete the more difficult main quest and advance to the next act.

In another improvement from Diablo, all of the quests will be available in both single and multi-player games.  The biggest difference between playing them alone or with friends is how they work with the party system.  When playing as part of a friendly party, as soon as one character gets a quest, it will appear in all the other party members' quest logs.  And when the quest is completed, everyone in the party gets the reward.  We don't know of many specific quest rewards yet, but none of them so far are a specific unique item.  If there will be such rewards is not yet known, since the party system would make that problematic.   Would everyone get their own identical reward item?  The problem there is that nearly every item in the game will be better suited for one class or another. If a quest reward is a sword, or a bow, or a staff, some characters will be much happier with it than others.  Even a ring or armour would be preferred by one class over the others, depending on the attributes of the item.  Certainly Blizzard North has taken this into account, and worked something out, though we don't know what yet.  We know all the quest rewards in Act One, and none are a specific item, they are all general benefits, like a skill point or the chance to upgrade one metal item.  How this is dealt with in later Acts is unknown.

Completed quests are "saved" to your character, so you need not complete them anew each game.  It is not yet known quite how this will work.  For example, there is a quest to rescue Cain and return him to the Rogue Encampment in Act One.  So if you had already finished this quest, would he already be in town the next game you began?   In that case would you be able to do the parts of the quest leading up to rescuing him?  Or could you do the rest of the quest, but when you got to the cage he was in in Tristram, would he be there, and back in Tristram at the same time?  The mind boggles.  One thing that is more certain is that with the saved quests, the better rewards will only be available to your character one time, such as the Act One quest, The Den of Evil, which provokes Akara to reward you with a skill point upon completing it.  This reward will only be available the first time you complete the quest, since it would be exploited otherwise. Obviously not all quests are saved, since clearing out major areas of the act, and killing various bosses are quests, and if they are saved and not available each game, that would take a bite out of the replayability.

Early info about projected quests in Diablo II suggested that some might be more subtle in their rewards.  For example you would regain some lost item, and have the choice of keeping it for yourself, or giving it to one NPC or another.  The benefit of having the item in your equipment would have to be weighed against both NPC's being angry with you for not getting it for them, and in any event one would be displeased no matter what, since you have to choose which one to give it to. An interesting idea, but there is no confirmed information about such a quest at this time.

Act I

The main quest in Act One is to find Andariel, in her throne room deep under the Rogues' Monastery, and defeat her and her army of minions. This quest is given to you by Deckard Cain after you rescue him from Tristram. After defeating Andariel, Warriv will take you in his caravan onward to Act Two and the city of Lut Gholein. There are of course numerous other quests in Act One, most of which we know something about.

The Necromancer at the entrance to the Den of Evil

Location: Blood Moors
Type: Clear area (kill all the monsters)
Occurrence Rate: Guaranteed
Given By: Akara
Reward: One Skill point, Akara will then open her magic shop to you.

This will be the first quest in Act One, and is one of the simpler ones. It is given to you by Akara, the religious leader of the Sisters of the Sightless Eye. She is located in the Rogue encampment along with most of the other Act One NPC's. You need merely follow a winding pathway from the Rogue Encampment to the burrow-like entrance of the Den of Evil, descend into this cave level, and kill every last monster in it.  The monsters in the Den aren't especially nasty; mostly zombies, skeletons, some Fallen, and a few larger creatures including the newly-named Yeti, a monster formerly known as a Gargantuan Beast. After completing the quest Akara will reward you with one skill point that you may use as you like.  Also, you will now be able to trade with Akara.  Her shop stocks potions, herbs, and other such items, and she buys and sells.

Blood Raven fights back

Location: Just off of the Cold Plains
Type: Kill the unique (Blood Raven)
Occurrence Rate: Guaranteed
Given By: Kashya
Reward: Can hire mercenaries (expensive!)

Blood Raven is not a scarlet crow, but is an evil heretic Rogue Priestess, who you must kill for Kashya, the leader of the rogues.  Religious conflicts are always bloody.  Blood Raven is very fast, has the ability to resurrect the undead (if that makes any sense.) and she can fire regular arrows and fire arrows.  However she doesn't have a ton of hit points, so if you can corner her, or just keep after her, you will triumph.  The reward for this one is Kashya granting you the option of hiring a rogue mercenaries to assist you.  However this is very expensive, probably too expensive for your low-level character at this time. Kashya will offer several rogues to choose from, each differing slightly in capability. Although they have their own AI, you can direct their movement and also specify targets for them. The word from Blizzard North all along was that you would only be able to have one hireling at a time.  However a recent Diablo II preview stated that hiring more than one at a time was possible, financial resources permitting. The ability to hire a mercenary will come if you reach a certain Clvl also, but this is a way to get it sooner.

Location: Stony Plains, Dark Wood, Tristram
Type: Find item, rescue Cain
Occurrence Rate: Guaranteed
Given By: Kashya
Reward: Cain will identify items (for free!) once you rescue him, and also provide much information about the various quests, just as he did in Diablo.

First you must find the Tree of Inifuss (in the Dark Wood), and touch it, which is easier said than done, since there are hordes of monsters around it.  The tree will then drop a scroll you must retrieve and take back to Akara.  She will read it and provide you with instructions on how to use the Cairn Stones in the Stony Plain to open a portal back to Tristram, where you must rescue Deckard Cain, the Horadrim sage from the original Diablo.   Tristram has been razed and is now infested with packs of Carvers, Fallen Shaman, and undead, including a unique zombie whose name you will remember from Diablo.   After rescuing Cain, you must lead him back through the portal to the Rogue Encampment, where he will remain and identify items for you.

Location: Stony Plains, Black Marsh
Type: Find Tower
Occurrence Rate: Random
Given By: Moldy Tome in Stony Plains
Reward: Unknown

This quest is not given to you by anyone in the rogue encampment. Rather, you will find the quest originating item, believed to be a book, somewhere in the wilderness (Stony Plains) and it will describe the task you need to undertake in order to complete it. Apparently after you get the quest from the book, you need to locate the tower, which is situated in the Black Marsh. It is not known whether on entering you will need to kill a unique monster, retrieve an artefact, or clean it out completely, like the Den of Evil.

Location: Monastery
Type: Find item
Occurrence Rate: Random
Given By: Charsi
Reward: Upgrade one metal item

In this quest, somewhat reminiscent of the Anvil of Fury from Diablo, you must fetch from the monastery a sacred armourer's tool called the Horadric Maul. With the maul, Charsi, the rogue blacksmith (seen here in a screenshot with the Barbarian) will be able to fashion higher-quality weapons and armour. Retrieving it for her will allow you to choose one of your metal items to be upgraded by her.   Another possibly might be keeping the Horadric Maul for yourself, or possibly selling it, though you would then have to deal with an angry blacksmith, who you need to repair your equipment and buy and sell items from.

Andariel prepares to swipe

Location: Monastery
Type: Find then Kill Andariel
Occurrence Rate: Guaranteed
Given By: Deckard Cain
Reward: Access to Act II

Andariel is in an inner room, deep under the Monastery, surrounded and protected by a mob of powerful servants, something like Diablo was in the first game.  She will not be an easy kill, with her poison ranged attack, and a vicious melee strike as well.  If you successfully defeat her, and return to talk to Warriv the Caravan Master, you may then journey to the second Act in the caravan.   Cain accompanies you to Act Two on the journey to Lut Gholein in the east. (Pic One, Pic Two)

Act II

While most of our information on quests is from the PCXL beta event and is therefore just on Act One, we also have information about quests that was released in a Gamespot preview, and of course Blizzard has released some info on various Act Two quests as well. 

The varied levels in the second act will include the desert wilderness, the harem beneath Jerhyn's palace, the city's sewer system, the Queen Maggot's lair ("insect lair" in GameSpot preview), and the Horadrim tombs. The harem will be the focus of one quest, as will the sewers and the Queen Maggot's lair. The Horadrim tombs are where Tal Rasha and Baal reside. They consist of seven tombs only one of which contains the Lord of Destruction and the Horadrim initiate. The other six are reported in the GameSpot preview to be filled with a myriad array of monsters and traps.

The Paladin exploring the corrupted Harem

Infested Harem
Jerhyn, the ruler of Lut Gholein, has had his royal harem, under the Palace of Lut Gholein, overrun and infested with evil.  You must first do something for Jerhyn to prove your trustworthiness, and he will then grant you access to his Harem.  We assume there is a quest in the harem; perhaps you must cleanse it for him, killing everything inside, like the Den of Evil quest in Act One?   Or maybe he desires some item left inside it returned to him.  Unknown.

Queen Maggot Lair
Though we don't know who gives this quest, we suspect that the goal of this quest is simply to kill the Queen Maggot. Also known as the Sand Maggot Hive, the entrance to this area is found in the desert wilderness, and looks something like a very large gourd, dripping a green ichor from the stem.  Inside you enter a level of smooth, straight tunnels, carved from the sandstone by the enormous queen maggot.  We sighted her at E3, and she was indeed very impressive.  She will be found deep in her lair, well protected by her offspring.

A City Guard

Hire Mercenaries
Griez, the captain of the mercenary guards, is in charge of the defence of Lut Gholein. Completing a quest for him will help convince him to lend you some of his warriors.  The specific nature of the quest you must do to convince him is unknown at this time.

The Paladin at the entrance to the Sewers

The Sewer System
Though we know that there is some sort of quest in this area, no specific details have yet been released.

The Horadrim Tombs (of Tal Rasha) - Defeat Baal
There are actually seven separate Horadrim Tombs in Act Two.  Tal Rasha is buried deep under one of them, but which one is randomly chosen each game.  We suspect that the tombs will be similar, perhaps three or four dungeons levels each, with the lucky one having some sort of an entrance that leads down to yet deeper levels on the way to Tal Rasha.  So you can either search through level after level of monsters and traps in each one, or there will probably be some sort of quest to find a map, or convince an NPC to give you directions, to the correct one.

Once you find it, there will likely be a twist.  Baal was trapped by a broken soulstone, the shards of which had to be driven into the chest of Tal Rasha, a Horadrim Initiate, to contain the demon.  Tal Rasha was then chained deep under the surface of the desert, in a great tomb, buried alive.  His sacrifice enabled Baal to be trapped for many years, but Tal Rasha is locked in an eternal struggle against the Lord of Destruction for dominance in his body.  Your mission in this quest is to keep Diablo from reaching and awakening his brother, or possibly to keep Baal from overpowering the spirit of Tal Rasha.  Baal in the body of Tal Rasha would be an extremely formidable enemy, with his demonic powers amplified by the great magical abilities of Tal Rasha.

Act III and Beyond

After completing the final quest of Act Two, Meshif, an NPC captain of a ship located dockside in Lut Gholein, will sail you further to the east, as you apparently follow the Wanderer to Kurast, a small town near the massive ruined temple of Travincal, deep in a tropical rainforest.  Mephisto, imprisoned in his soul stone, was buried deep under the temple, watched over by the order of Zakarum.  However the Cult of Zakarum has lately been corrupted by powerful evil influences, and have turned from guards to protectors of their deep secret.  You will come into conflict with the Zakarum in Act Three.

Very little is known of the quests in the third act, and nothing at all of any quests in The Finale.  In Act Three it is believed that defeating Mephisto, the Lord of Hatred, will be the primary goal, thus the setting for the final quest is believed to be the temple of Travincal. Likely there will be quests related to cleansing other temples of evil, or fetching sacred artefacts, but all is mere supposition at this point. However some info was gleaned from the recent GameSpot preview.

Ormus The Mad Poet
In between his mad sayings he will offer interesting and often vital information about the Diablo 2 storyline. He also is the originator of one of Act Three's six quests but the nature of the quest is unknown at this time.

Asheara
Serving a similar role to that of Kashya and Griez in the preceding acts, Asheara, believed to be seen in this recent screenshot, is the leader of the Iron Wolves, a group of Act Three mercenaries. If you complete a quest for Asheara, he will hire out sorcerers that will then join you in your third act travels and provide you additional support with their magic skills.

And when the quests are done?

Once you have finished the game, quests and all, the game is by no means over.  As in Diablo I, Diablo II will have multiple difficulty levels, and of course the random level generation.  Max Schaefer confirmed in our interview at ECTS:

"My guess is we're going to do difficulty levels just to handle the varying levels of players.  Once you've played for a few months, your character is super strong and you've beaten Diablo it really makes sense that you have a difficulty level to increase the challenge".

In addition to that Bill Roper has flaunted the proverbial Red Rag to the hardened players by claiming, "It will be very difficult to get beyond level 50, but there is no hard cap on experience levels". With a promise of cheat-free Battle.net games this will truly be an achievement.

As well as set quests you can set your own personal quests also. Finding the Holy Shield of Defence, for example, and deciding that these are the attributes you are after will set your own personal quest to find a Holy breastplate of Defence and the Helm or mask to match. Getting all three isn’t just some fashion coup though, your perseverance for a full set of equipment will be rewarded with a healthy bonus, not to mention the pose-factor when hanging out on Battle.net.

And if that is not enough, Blizzard North has spoken of releasing new quests for play over Battle.net on a semi-regular basis, and Matt Householder of Blizzard North has hinted that they hope to release a Diablo II expansion pack, which would add additional Acts, as well as more quests to the existing ones.

This page has been taken from Diabloii.net. For more info go please there. (it's far better then this page)