Fun game and very addictive! I really like the style of the graphics, and the idea of the shotgun wizard.
At times it's a bit difficult to tell what's going on, especially when there's a lot of dead guys on the ground. Perhaps that's even intentional, it certainly adds to the mayhem. Also I find the font in the upgrade buttons hard to read.
These are my first thoughts, I'm going to pay this more later when I have the time