It was upconverted.
As that article states, the live action was shot in 2D, but the CGI was rendered in native 3D, so I guess it's kind of a hybrid.
I loved this film. I think one reason was that there was no baggage to it. There was no "Oh no; they screwed up Superman!" or "Hey, this is not Star Trek!" It was obviously inspired by specific things, but the mix was unique.
And there was some genuine wit throughout, and the human characters, while archetypal and not particularly three-dimensional, were not annoying (like those in, say, the Transformers movies). Even the two scientists grew on me after a while.
I also appreciated the brief nod to Ray Harryhausen and Ishiro Honda at the very end.
Edited by Bryan Tuck, October 12 2013 - 10:13 PM.