In the Red Version of Pokémon, almost nothing is different except there are certain Pokémon that you can't catch that you are able to in the Blue Version. You need both versions to catch all 150!

Here are the Pokémon that you can only catch in the Red Version.

Ekans	Arbok	Oddish	Gloom	Vileplume	Mankey	Primeape	Growlithe	Arcanine	Scyther	Electabuzz