RE6 was awful, a friend and I couldn't even bring ourselves to finish it on co-op, it just dragged on and on and on. The storyline was more absurd and convoluted than anything Hideo Kojima could come up with, the characters, script and voice acting (despite having some talented names) were poor, and the gameplay was horrendously repetitive. Stupid QTEs which were made even harder on co-op if there was any lag between the two of you.
For a game that was clearly designed around being co-op, it was completely silly that you had to start the game as a solo player and complete the first bit before you could actually do the co-op bit.
For a game that was clearly designed around being co-op, it was completely silly that you had to start the game as a solo player and complete the first bit before you could actually do the co-op bit.

I really enjoyed the 4 different campaigns it almost felt like 4 games in one (a long requested feature after the "his" and "hers" discs of Resident Evil 2. The increased focus on melee was a fun change and it was only really appropriate to use in small groups so didn't make the guns redundant.
I think they tried to make them all different in the hope people would enjoy it and not be bored with the same enemies and locations but I'd rather have one awesome campaign instead of one that was enjoyable and the rest 'meh'