That said, I don't think the IMAX really was essential. For having a huge screen perhaps, but there wasn't anything about it visually native to IMAX. You could sit really close to an average theater screen and have the same experience.

Except for the sound. The sound was intense and well executed in an IMAX theater. o_O

As for 3D, it is worth seeing in 3D. It was filmed 2D and converted in post, but the conversion is as good as it would get, I think. The IMAX 3D theater projection hardware would still be the best setup for seamless 3D immersion (as it is for any 3D film) (as opposed to active shutter, or single-projection flickering) - smooth and natural 3D (aside from being faked :P)

My recommendation: see it in a quality 3D theater - not necessarily IMAX unless you're willing to dish out the extra for the bonus boosts in sound and smooth 3D quality that IMAX is good for.