Game: Gunbrick

If you want to be a retro looking game and play in a 50 pixel by 50 pixel space, then really you need to be pretty simple. There's only so much that can go on in such a tiny spot. In Gunbrick, you play as a tiny square who can rotate left and right with the keyboard and fire a gun that sticks out of one of your four sides. You can't move the gun, you can only change which direction it's pointed by rolling around. It's a unique mechanic and it's put to excellent use over the course of the game.