Any thing about this is perfect! The movement feels intuitive and understandable. The music sounds awesome and fits perfectly into the gameplay! The animations, especially of the humans, are geniously hillarious.
The only thing I'd really suggest would be a crosshair as it sometimes is hard to see where you're shooting. Especially as it isn't the dead center of the screen...
This will definitely be something I'll return to if I have a few minutes to spare!