I'm glad I read the comments about how to use the weapons, at first it wasn't obvious and wasn't much fun. But after understanding it that terms out to be the main (for me) feature of the game!
It was satisfying get a stack of them and taking out waves of enemies almost instantly. :) But then it because monotonous and I didn't see what my next goal was. I let the enemies attack me and the crystal for a while but nothing much happened?
Great start to a game though, especially the attacking stuff. Well done!