Haven't played it in forever due to some glitches,
Castle Crashers is an amazing 4-player beat-em-up. It has a great art direction and plenty of classes to choose from. While it's a bit repetitive, it's a beat-em-up, and that's their nature. Online was plagued with bad connections and taking forever to find a group, but hopefully that's all fixed by now. If it were never a problem, I'd still be playing it now. The only thing it does bad is it goes overboard with toilet humor, but it's slightly funny the first time around.