cool concept for a game

Love the concept ! Could really use a bump in difficulty, though-- hearts are way too abundant.

Maybe an item shop ?

wow nice

Firing a massive amount of bullets and the sound it makes feels very rewarding.
Though I think the game would be more interesting with far less than 100 bullets, as I never ran out.

Unfortunately, having to replay the entire game because I died once discouraged me, especially since I lost a lot of my health to two spikeballs that kept pushing me back & forth. I understand that there is knockback, but at least allow me to keep moving my character.

Having a lot of health also means it takes a lot of mistakes untill you die, unless you get cornered after which it's over before you know it. I would reduce the amount of health, and push back all nearby enemies when you take damage.

Speaking of enemies, while they are quite interesting, they do not form much of a challenge.
To make the blue slimes an actual danger I would also let them eat bullets that lie on the ground. Besides, I would color the bullets they shoot at you in a different color, as I was confused at first.
I also think that the armadillo's should be invincible and reflect bullets back when they are in their ball-form, because currently you can kill them before they can reach you.
Furthermore, I think enemies shouldn't attack you only when you come within a certain distance, because now you can just shoot at them from a distance.

Finally, I understand that the boxes in the room add more things to shoot at, but having to pick up hearts is obnoxious and doesn't add anything to the experience (especially since they block bullets, preventing them from hitting boxes behind them). I would just let them fly to you once you've destroyed the box.

It was a fun game, but it also has a lot of untapped potential.
So I hope this helps :)

Lame S#!7.