I have to say the best betrayal I have seen was in Beaten Kaos, I doubt anyone could see it coming and while their might be some small plot holes that could arise from it while I was playing it I had no problems.
About the "game needs to be judged on single player" argument. Personally I tend to fall into a similar camp as you, I predominantly play single player games and when I play multiplayer it tends to be in the form of hanging out with friends instead of with racist 13-year-olds on line. But I feel that you can't necessarily say that games need to be good single player games to be good. Team Fortress 2 is great despite no campaign and what about non-video game media such as playing a trading card game or a board game, they obviously only work with other people, why can't a video game be built on the same principle.
About the "game needs to be judged on single player" argument. Personally I tend to fall into a similar camp as you, I predominantly play single player games and when I play multiplayer it tends to be in the form of hanging out with friends instead of with racist 13-year-olds on line. But I feel that you can't necessarily say that games need to be good single player games to be good. Team Fortress 2 is great despite no campaign and what about non-video game media such as playing a trading card game or a board game, they obviously only work with other people, why can't a video game be built on the same principle.