I'd have to say forced co-op. It's been my least favorite thing about this series since RE5 and Capcom seems to have no intention of dropping it. Even in Revelations, a game with no actual co-op in the campaign, an AI partner was forced onto us most of the time. I have no idea why.
RE4 was one of the best single-player experiences I had with a third person shooter and I doubt I'll get to experience that again because of Capcom's idiotic AI implementation.
"I hate you, UncleWesker. No, really. You are the biggest douche on this board. You should go hang yourself in your basement." ~ RT102
The thing i hate the most about this game is that i bought this steaming pile. The story is a mess. The new characters are a waste The game itself is linear and boring. Way too many QTE's Driving segments are so very awful. Jake Muller needs to never be in another game ever again.