Schizoid

In Schizoid, which calls itself "the most co-op game ever", a red ship and a blue ship battle red and blue neon glowing enemies. The red ship will destroy any red enemy it touches, but will be destroyed by any blue enemy; and vice versa for the blue ship. The result is that the red and blue ships must work together closely to alternately guard each other and smash enemies. Lives are shared, making this a pure co-op experience for 2 players - or 1 player can play with a computer AI, or control both the red and blue ships simultaneously with the two thumbsticks in the hardcore "Uberschizoid" mode.

Schizoid has 119 levels, divided into 7-level "chambers" with a save checkpoint at the end of each chamber. If you beat a level without any life losses, you get a gold star on that level; whenever you lose all your lives and go back to the last save checkpoint, you will skip past any level you've "golded", providing a big incentive for completing a level perfectly.