Depends on what you're meaning? Biggest game so far, or biggest game to come?
So far, It was DA2. I was a little disappointed in a few areas it is safe to say, but followed development and was really excited prior to its launch.
The one to come, was ME3. However, since this has been pushed to 2012 and no longer qualifies, I would have to go for BF3. Im not a big FPS player tbh, but really enjoyed Bad Company 1 and 2. BF3 just looks amazing, as others have said.