Star Wars: The Empire Strikes Back is a pretty good game.  It's similar to the game "Defender", but it has quite a few differences.  You pilot a Snowspeeder on the frozen planet Hoth.  Your mission is to try to destroy a line of giant Imperial Walkers, also known as AT-AT's, (which basically look like giant, skinny, mechanical dogs) before they reach the rebel base (you're a rebel).  You have a radar at the bottom of the screen which lets you know how close the walkers are to your base.  It takes 48 to blow one up unless you hit them just right, but they are kind enough to change colors to let you know how you are doing.  They start off black and turn red then orange through a variety of shades as you get closer to destroying them.  Every once in a while, you are overcome with "The Force" and can's be hurt for a few seconds.  You will know that you have "The Force" because music will start playing and your Snowspeeder will start flashing.  Overall, this isn't a bad game.  It is the easiest to find of the Atari 2600 Star Wars games.