Easiest or quickest?
Transformers: Dark of the Moon was an easy one at about 6 - 7 hours (including the online). Megamind was easy and quick with the exception of that damned glitch, but that also came out in November 2010
I was going to say Truth or Lies, but that came out in September 2010. Mayhem was easy if you don't count the last two races (came out in March 2011, around 5 - 6 hours). Also, Cyber Troopers Virtual-On Force, which is Japanese but region free, was extremely easy (took me about 5 hours). But that one came out the last week of December 2010.
For sports games, Madden 12 and NCAA Football 12 took me about 10 hours each. Lego Pirates, while very easy, took me 25 hours. Lego SW The Clone Wars took me around 30 hours, but was also easy.
Man vs. Wild, Captain America, Green Lantern and Cars 2 are other easy ones at about 5 - 7 hours each.