Some of the previews before the movie were in 3D, so I experimented with taking the glasses on and off to see the difference. The most noticeable thing (besides the fact that without the glasses everything looks like blurred copies of red and blue version of the movie) is that 3D is dim. I imagine that this is because light is filtered out by the polarization of the glasses.
My verdict: There were parts of the movie that were improved by the 3D conversion. The pod race and fight with Darth Maul were even more thrilling in 3D. When the exile Naboo government seeks out the refugee Gungan government, the 3D is impressive—someone went to the trouble of making each and every fern plant 3D. However, in other scenes entire blocks of background are made 3D together, giving it a flat appearance. In fact, 3D in general seems to make things look flat, but at different depths. Also, I observed that there is a range where the 3D looks good. Too 'close' to the viewer and the two images still look separate; too 'far away' from the viewer and things look flat.
Setting aside the 3D conversion, my one real complaint about this movie is that it never explains why Darth Sidious wanted Naboo under the control of the Trade Federation (the eponymous phantom menace ). He even commanded Darth Maul to make sure that Queen Amidala sign a treaty of surrender (which would be valid under Galactic law). So, despite what others claim, it wasn't just a ruse to generate a sympathy vote in his bid for the chancellorship—that was merely a serendipitous side-effect which he astutely took advantage of.
 Read my review of that film here.
 Before this, the only 3D film I'd seen was IMAX Wild Ocean 3D at the Moody Gardens (see here) in Galveston, Texas, while Leann and I were on our honeymoon.
 Though you could argue that the title of the film refers to Darth Sidious and/or Darth Maul.
Hubble Ultra Deep Field is by NASA (and is in the public domain), available at http://en.wikipedia.org/wiki/File:Hubble Ultra Deep Field part d.jpg.