Avatar definitely had great 3D IMO. The tech/effects were the main reason to see the film, and will be pretty much the only reason I see the sequels.
I've seen a lot of other films in 3D since then, but it didn't really help many of them, and seeing them in 2D would have been fine.
However, in November I saw Doctor Strange in IMAX 3D, and that shit was crazy. It wouldn't have been quite as effective in 2D IMO. That was a trip.