Game plan.

After thinking it over, my game will be simple but hopefully fun. Basically, you just wander around in a procedurally generated cave, trying to bring life back to it.
Everywhere you go, plants start to grow again. But, you'll have to fight off the evil creatures already living there. Your only defense is the life that you cause. The more plants in an area, the more defenses you have. If you successfully bring life back to the entire cave, you win. But, the cave itself also mutates as the game progresses, so you'll have to work fast. 

I deliberately tried to make the gameplay as simple as possible since I have a nonexistent chance of finishing already, and so I could add music!