excellent combination of leveling system and action, where grinding is rewarded but neither replaces the need for skill nor is mandatory. this is how "upgrade" games should be.
my main gripe is that you're forced to stop killing things whenever you level up, causing the gameplay to lose all momentum. and it happens very often. it's annoying and should be optional.
by the way, I can't help but feel that the eye is underpowered due to eye only levels literally being impossible to beat. hey developer, you actually ever beat them yourself? I don't buy it.
there is no reason for the left click button to be used in a game where you don't otherwise use the mouse at all. just let us reconfigure it to something else please so we don't have to accidentally keep clicking outside the window or on the logo on the bottom of the screen. please.
that was fun. and, as I decided while I was fighting off a horde of monsters with my farts, just plain silly. one beef: too easy. though this is way better than if you made the game way harder by just making the upgrades really expensive or something.
PS: I hate that nailgun.