I love the game, and especially the 2.5D visuals! Also the variety of enemies and bullets which deal more damage to certain enemies. It's a great concept. I would add some kind of description though, so you know what enemies are weak to, or what bullets are good against.
A good improvement would also be some feedback for when you get hit, like a camera shake or similar.
Also a funny thing, you can still shoot and move after dying :)
Anyway, great game, keep it up!