Main thread here.
This should be the penultimate preliminary unless there are any other series that desperately need one. I can see this coming down to what your interpretation of game of the generation is. Does it mean the most influential game (probably Gears 1)? The 'best' game in terms of features and gameplay (probably Gears 3)? Or just your personal favourite (for me, Gears 2)? It's up you to decide what you want game of the generation to mean. Get your votes in by midnight GMT/4pm PST.