Take a classic approach on a shoot em up, and add a frustrating twist to make a whole new game.
Inside a Star-filled Sky is an overhead shooter with interesting gameplay.



Don't like an enemy's powerups? Go inside of it and change it to something weaker.
Want a more powerful powerup, go inside of it and make it powerful. Pretty soon you'll forget where you are, and you'll lose track of what you were doing.
"Was I in an enemy because I was stuck?"
"Where am I again?"
"Am I sixteen levels into an enemy?"
As you go higher, it gets harder. Enemies get more powerful then you, they become unfair and start using tactics.
http://insideastarfilledsky.net/http://www.youtube.com/watch?v=pQaIAhHJvAw&feature=player_embeddedIt's twelve dollars. Completely worth it if you love hard games.
(BTW the same guy who made this made Sleep is death)