Before my family first saw it (in standard 3D), my younger teenage son was cynical, claiming that it was way overhyped and couldn't possible measure up. We basically had to drag him to the theater. After the movie, both he and his older brother said they wanted to see it again.
My sons and I did see it again, this time in IMAX 3D.
We all agreed that the movie was just as good the second time around.
None of us felt that the IMAX visuals were significantly better, but we all thought the sound was much better.
I haven't seen the non-3D version, but in my opinion the 3D is not overdone, i.e. there aren't things popping out of the screen to grab your nose.