I really like your prototype !
Here his a few things I noticed during my test :
- You cannot go both horizontally et vertically in the same time, based on the feeling I had playing, it seems to be a game with a good pace, and being able to move diagonally seems to fit that fast pace vibe.
- If you go past an ennemy, you have to go backward to shoot it. It can be interesting to be able to flip the player.
- I didn't see what happens to the player on being hurt (except the effect of course), I assume you would lose some time on the timer.
Overall I think you really have a good concept, keep up the good work !