Yet another upconversion. I personally haven't seen it in 3D yet, so let me know if this verdict is wrong, but I would say don't bother with the 3D, it will probably dissapoint.
I saw it twice, once in 3D during the Iron Man marathon (with 2D IM & IM2, and 3D Avengers and IM3), and then again in 2D. Great movie, but after seeing the Avengers in 3D (again) IM3 felt flat. I don't recall even noticing the 3D, and it certainly didn't lose anything in 2D.