I like top down shooters, and this was fun to check out. I like the structure of the game (moving quickly from level to level), and with a few tweaks and fixes, it could be good.
Some of the maps (are they randomized?) were tricky to play because you got stuck against a wall, and shooting enemies up close doesn't work too well. I think if you fixed up the collisions, it would be a smoother experience.
You could add more animation, sounds etc. to help replayability and have it be more satisfying. The weapon sound was a little repetitive for example.
It was fun to check out overall. I thought a mix of ranged and melee enemies was good. Having different weapons helps, and you could add crazier guns and enemies.
Keep it up!