As a few people have said, the speed is far too slow. But aside from that, this is great. You've obviously put a hell of a lot of work into it, and the introduction of power-ups is a very nice touch.
I gotta say, I found the co-op to be okay. The CPUs aren't the smartest, but most of the time they were useful. In fact I found Ep 4 to be easier than Ep 2 and Ep 3
Good game. Quite a bit to it, which raises it above the norm. On an unrelated topic, what's going on with this board; spammers and admin deletions all over the place?