I had fun with this game! But there were still some kinda ehh things I noticed.
Hate to say it, but I think the controls are kinda bad. :( Not being able to backpedal in a top-down (well, kinda top down :P) shooter makes it feel awkward since you can't aim at a bad guy without either standing still or moving towards them. Being able to shoot and dodge at the same time would make the movement more interesting and less frustrating, in my opinion. That being said, the shooting is good. The slowdown after each kill feels great and lets you more easily dodge incoming bullets, which is awesome I think. :)
I also noticed that, because of the level geometry, if you stand on the edges of the arena you shoot above the enemies instead of hitting them, so that's a small oversight.
The rest of the game is solid. The graphics are clean and cool, the camera angle is a little jarring but looks nice, and the music is excellent! Swapping weapons all the time is exciting and frantic, perfect for this kind of game.
Overall I'd say it's a good game! It would be really good, maybe perfect, if the control scheme felt better to play with. As the developer, it probably feels very natural to you, but as a player it's tough to look past. Having just one usage per weapon is enough for it to fit the theme IMO, so I don't think having everything on the mouse was worth it. Of course, for a 48 hour game it's fantastic. It might be worth it to try and get a beta tester next time, since you've already got music, art, and code down tight :)