I havn't played a co op game in a looooooooong time. As the answer to your question, I sometimes find it odd to play in co op. Mainly because I trust my muscle memory skills with the game (referencing your previous quote about muscle memory) so then I know that I won't mess up. However, if my co op player does mess up ten it would frustrate me, I'd have to baby sit them until they get through their part and then I can do my part quickly