What do you mean, there's no real co-op?!
1 – Grand Theft Auto Series
While GTA IV had some pseudo co-op modes, what Rockstar has always excelled at was their exposition. Their ability to drive a player deep into control of a character is amazing, and Niko Bellic in GTA IV was an engaging fellow. But the game also contained plenty of other great characters, perfectly suitable for co-op. Tack onto that the amazing depth in mission design, taking into account a second player, and you can really get into some fresh territory in terms of gameplay.
With several other open world games adding co-op gameplay, including Saint's Row and Mercenaries 2, Rockstar almost has no choice but to add this to their next GTA game. And while we had hoped to see something in their exclusive DLC for the Xbox 360, it looks like it's not going to happen.
There's still hope for the above games, with quite a few sequels on the way there's plenty of room for co-op. Just look at some of these upcoming and recent titles as examples: Ninja Gaiden Sigma: 2, Red Alert 3, Dawn of War 2, 50 Cent: Blood on the Sand, Resident Evil 5, Fable 2, Lost Planet 2, and Uncharted 2!