The concept is definitely there. It reminds me of the golden age of flash games, with lots of fun little cartoon puzzle games. If this got a bit more polished I could definitely see myself playing through a longer version.
A few things I would change, It wasn't very clear what was killing me sometimes---I would just be moving along and suddenly the level restarts. The enemy bullets could also be a bit clearer, and maybe they could have attack animations.
The physics needs a bit of work as well. At the moment, there are some issues with getting stuck in corners, getting stuck fallen over, etc. I think it would also be fun if you made gravity weaker or made the gun more powerful. To get around I kind of need to spam it, although I don't know whether this was intentional or not. I also don't really understand the reason for having a bullet limit, although that's my preference.
Finally, on the third level, when I killed both the guys and got to the door, nothing happened. I'm pretty sure this is a bug.
Overall, I think this game could be really fun with a bit of work. The framework for the gameplay is in place, and the art is quite fun.
Happy jamming!