I think this would be way more fun with a better level layout. Right now, it's too easy for my ally to get stuck in the lower part of the scenario, leaving me alone against the horde of enemies. I change the player to move the stuck one to the upper side, but then my AI ally falled and the cycle repeats.
Even so, I think the "two guys against the world" mechanic is nice. When I understood the game, it felt fun for some time. Having an actually acting ally instead of a passive one is cool.