I am eagerly waiting for Assassin's Creed 3. Although AC was repetetive and surely had some other flaws, I still loved it for what it was: simple, great gameplay in a beautiful and unconventional setting (for the most the strongest point of the whole series). AC2 feature all of ots predecessor's strength and erased improved on all of its shortcoming. Especially at the beginning I found the world much more engaging simply because there was a deeper connection to NPCs than in the first installment, simply because they were your family.
After Ezio's father died and the family escaped from Florence Ezio was rather disconnected from the rest of the family. From that point on the story became centered around Ezio and the politician he had to kill. While there's a lot of intrigue, scheming and betrayal going on, this doesn't affect the player or the gameplay at all.
How can a game create the feeling of betrayal in the player, rather than just in the character? Suppose you have a single player game with a character named Bob. In a Resident Evil 5 manner Bob has a companion named Alice, who is a playable character for Co-Op mode.
At one point in the game, Bob and Alice part ways. In Co-Op this not only means that the players don't see each others characters, this also means that all communication between the players like voice chat is cut off. For just one "level", say half an hour or so.
At some point after the seperation Bob's mission is to disguise himself as Christian -- a character unknown to the players -- and attend a cocktail party to get some information. Alice, on the other hand, is assigned to kill someone on the cocktail party, someone called Christian.
When Bob, in the guise of Christian, sees Alice, he'll probably try to make contact with her. Even if not, the player will not feel threatened at all by her presence. He'll rather feel happy to see her again and be excited about talking to player 2 again, who probably is his friend. Alice, on the other hand, will not even know that player 1 is present on the party. And because player 1 isn't aware of any danger, player 2 has no problems in taking out Christian, i. e. Bob, so that player 1 will undoubtedly feel this as some sort of betrayal.
Of course this is not the end of the game. Bob survives the attack with the help of Dorothee, who is his companion from then on and can be played by player 2. And there are more ways of how to elaborate on this idea. For example, the players could be seperated more often before that scene and happily reunite, so that they don't have a clue what will be happening.
The game could also offer player 2 the choice of how to proceed:
a) Stay with Alice and play disconnected from player 1, but still in the same game session. Simultaeous single player is the term that comes to my mind.
b) Play Dorothee for standard Co-Op.
c) *happy for ideas in the comments*
This is just a short blueprint. While there are of course drawbacks to such a scenario -- Alice's story essentially becomes a second game after the betrayal scene, technically this all might difficult to implement and so on -- I think this approach to Co-Op play certainly has potential.
"I wanna see some games!" (Johnny Chung Lee in Head Tracking for Desktop VR Displays Using the Wiimote)