Simplicity: Very simple.
Fun: Not crazy fun. The actual shooting is fun, but babysitting the AI isn't.
Creativity: An entirely unique idea.
Visuals: Not too good, but the other things more than make up for it.
Sound: I loved the music.
On Topic: It feels as if the AI is just a thing you have to babysit and upgrade. You can't even shoot at the same enemies as them, just give them stuff and have them handle it. Cooperation is two way.