Needs major balance pass. Exp is pointless, shotguns are overpowered for their price point. Needs "click outside of the window" detection. Last level is completely jarring when compared to the rest of the game, some sort of difficulty ramp would be nice. Otherwise? Awesome. 4/5.
Lots of potential. Lots of things to fix.
Fix movement speed. Rebalance levels so it is not as easy to get stuck beyond hope (getting trapped on the first level and having to suicide while figuring out how to play? *bad*). Fix detection of platforms so you don't get stuck in the middle of them.