I liked how the scaling of the enemies and yourself makes the game feel more climatic as the game goes on. If you are taking suggestions, I think two things could help improve this a lot.
1) It would be really nice to have holding the mouse button down continue firing. Maybe I am weak, but near the end of the game my finger was feeling sore.
2) I think some enemy variety would be nice to help vary up the action.
Thanks for the game!