Felt a little rough when I first started but when the game clicked it hooked me, I kept wanting to jump straight back in for another go. The sound effects of killing the enemies and picking up the crystals was so satisfying.
The little indicator which pointed to the next crystal really help solidfy the whole thing, since it gave each run a sense of direction.
I also liked the detail that the bullets were universal, the ones you fired could hurt you, but also cause enemies to hurt each other. It really felt like a level playing field.
I really enjoyed this!