Brilliantly executed as far as sound and art go, and really awesome concept. The gun was brilliant, loved the overpowered feel of it, and was a lot of fun to play around with.
However, had a bit of an issue with sprites rotating on the Z axis - whenever I used the gun and got that super cool effect of being thrown back and blowing everything up, my character would end up facing in a weird direction, diagonally up or facing the other way diagonally. If you freeze their rotation on the Z axis, i.e. the axis going away into the screen and stop any rotating around, then the sprite will always stay on its feet facing forward. I think that would improve the gameplay experience quite a lot, as I often got stuck facing a bad way :D
Got a bit stuck behind obstacles after they've been blown away as well, so maybe you could make them not interact with the physics anymore once they've been blown up, or if you want them as new obstacles, maybe just design the level so the player can't get stuck behind them.
Great effort though, only reason I'm going on about the stuff above is cos I really enjoyed this and can see a lot of potential here, so definitely keep going with it ;)