Seems a lot of people are struggling to grasp what the word "influential" means in the context of this thread. I'm pretty sure Rob means the games that most inspired later titles to copy their features or themes. Not the ****y "FF7 influenced my life maaan, it's amazing" meaning of the word.
Gears of War being the perfect case in point. Every sodding 3rd-person shooter seems to have to include a in-built cover system now, for better or worse. Thus, it has been extremely influential on the rest of the industry.
Not too sure I'd agree on LBP though. Unique, yes, but I think most other developers have been off-put by the excessive complexity of it all, and the ease for it to get broken.
Also, I'd say the perk business in CoD was heavily inspired by BF2's unlock system, so I'd give that award to the latter.
In many ways, I think the most influential things this generation have been the consoles themselves, rather than the games. The 360 gave us awards and online leaderboards, the Wii motion controls, and the PS3 an incredibly developed multimedia system.