I've been playing coop with the wife lately. This game is fantastic. Its the best coop game we have played since Borderlands which we also loved.
There just aren't a lot of games that combine character development, open world, and coop. That feature set alone sets it apart from so much mediocrity.
I love the zombie genre, but hated L4D2 which is nothing more than a twitch coop shooter in a corridor environment that had zero character development and zero environment immersion. I mean if that is what you're into then the more power to you, but I'd even go as far as to say Fort Zombie is a better game.
Shame about the Ryder White DLC though. With no coop or character development its just not the same game anymore.