It's a question how good either were
MW2 has gotten endless howls from the PC crowd due to the changes in the multiplayer, while the console ports have fared better. But basically I felt let down, the single player I finished in one long evening, and the multiplayer is more like Call of Duty 4.1, not that big a change.
"Avatar" I think has this "Titanic" effect going on. During it's release people raved about Titanic, a lot of it due to the special effects, and today it isn't thought of so well. Ghostbusters also comes to mind, although I think that was more audience effect, seeing it on TV deflates it. I thought Avatar was a pretty stupid movie, yes, groundbreaking effects, but I honestly would have titled it "Dances With Wolves meets the Smurfs in Vietnam."