I got this when it was on sale for $20. The mp was pretty fun, but I stopped playing it after a while. Not sure why, I just didn't feel all that compelled to play it (likely because I had friends playing other mp games).
The campaign is very good imo. The first time I beat it was co-op at a friend's house (over the course of like 2 months) and I didn't find it all that great. But now that I'm playing it solo I'm really liking it.