I was lent this for a week while I had to go down to Wales. Just wanted to say something.
Single-player is poo, no doubt, it's a waste of time. But in offline co-op... It is one of the most fun games I've ever played. Seriously. The demo does it no justice whatsoever, they picked the worst level and it only showed how awful it is when you play on your own.
I find it very hard to get good offline co-op games, which is such a shame because the missus loves them. We had a great time with Gears Of War, we had a laugh with Rainbow Six Vegas (although they cut the story out when you play co-op, which was just ridiculous). The Simpsons Game was brilliant though. Very very funny, and with all kinds of genres mixed into it.
I couldn't get over how brilliant the games jokes were, they weren't just Pacman jokes and whatever, they were relevant to today's games. Brilliant stuff. If you've got someone to play with on the one Xbox, I would at least rent it and try to finish it in three days.