Excellent!
The graphics are very cartoony and stylish. The gameplay is great fun! Some suggestions, though:
-Make it possible to sell upgrades you don't like. Combining triple shot with boomerang didn't work for me, and I was unfortunately stuck with it.
-I'd like a more obvious health meter. The one in the corner combines health and distance to goal, and it can be confusing (unless it was your goal to make the player more vulnerable as they near the end of the level).
Those flaws aside, this is great. The weapon mods are really inventive, and I only wish there were more to choose from.