Fitting four players in Gears of War 3 was difficult, but Epic decided that the time was right.
Epic design director Cliff Bleszinski says that the four player co-op in Gears of War 3 was "pain in the ass" to design, because the three extra players complicate things in ways that would never come up in a single player game.
"You can't just assume the AI is going to be standing in this corner so that player one can come round the corner and see the amazing cinematic like in Dead Space or something," Bleszinski said. He explained that Epic had had to build bottlenecks into the levels, so that it could control exactly where everyone was at certain points in the game. He also said that Epic was concerned that very few people would make use of the four player functionality, but hoped that the arcade mode with its mutators would help to draw people in and give them a reason to go back and play through the campaign more than once.
Despite the difficulties involved, Bleszinski said that Epic had decided that the time was right for include four player co-op in a Gears of War game, and had taken a "Field of Dreams" approach to the co-op - "if you build it, they will come." He also said that despite the difficulties, four player co-op gave players the chance to play as someone other than Marcus or Dom. "One of the biggest benefits in that the only way you [can] play as Sam is to be Player 3 in Act 2 or as Carmine is be player 3 in Act 1. That's kind of cool in that you can see their perspective."
Source: The Telegraph