It is mind blowing in 3D on an IMAX screen.

Occasionally bothersome plot aside, I found it to be the most immersive movie I've seen in years, and I think it's largely due to the excellent 3D.

I've seen it now in both 3D and 2D. You lose some of the wow factor of the visuals in 2D, but it's still beautifully rendered either way.

I also found that the 2D seemed to have more color depth than the 3D, but that might just have been my eyes trying to adjust to the 3D glasses.

It might be because each eye only sees every other frame in the 3D version (assuming this is on a single projecter with an alternating polarizer and not two projectors with different film and different polarization).

No. It is a fun romp and visually gorgeous in 2D.