This is why I really enjoyed Resident Evil 5. Although it's not my favourite RE game in general, I loved the co-op aspect of it. Really good fun. I tried to play RE6 co-op, but ultimately it was just such a flat and uninteresting design that I couldn't get into it.

That said, I'd like to see more co-op RE games in future (and I mean, story-based games rather than the various multiplayer atrocities that get packed in for free with mainline games).