I've only played alone for 5 minutes while waiting for my other friends to finish their download, but I can tell it can get quite dull playing alone. But playing with two or three other people for coop on Sniper Elite difficulty is very fun. I do wish that there was more variations to the zombies that we kill. And definitely need an option to invite people midgame, and also disable or increase the idle kick timer, it's quite stupid that people get kicked after 5 minutes of idle.