I liked it!
Things I did not like:
The controls! I just hate this "aim-with-the-mouse"-concept. I feel, I can't aim properly, because the moving can "destroy" my angle. Also I click outside the game and die... I like the concept from Binding of Isaac much better. I think, it would fit the game well.
The upgrades: Felt useless, because there were so few. I think, it could be a nice game element, but at least in the short version, they are not needed.
What l liked:
Cool game in general! Good art, good music, good overall concept. Also, I liked the difficulty. Many games are just "upgrade, until you can blow everything away with one shot", and I really liked, that instead of that, you have to work on your skills and "learn" the rooms. Maybe one thing: At first, I thought, I had to clear every room, which made it a little tideous. Maybe, somehow you can clarify the goal..?
Anyway, thanks for this game, pretty cool!