3dont Only a couple scenes used the 3D well like the opening, Stark Mansion, and ending action sequences.
3do It was OK, but could be better. See it either way.
3dont 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.
3dont save your cash