Worth it for the experience, like Avatar. Story/plot (or at least the execution of it) was underwhelming, but I already had low expectations for that. They refer to things that happened in the extended universe, like the comics and video game leading up to the movie. Overall, it was miles more entertaining than the first movie, which really wasn't that hard to do. It's a fun ride.

At the beginning of the movie (IMAX3D) it says 'Parts of this movie were shot in 2D and were meant to be in 2D. But please keep your glasses on the whole time.' The 3D was pretty decent when it was used, but I don't know if I can recommend going 3D over 2D. IMAX only does it in 3D anyway, and I wanted to see it on that big screen.

Also it was surprisingly violent--I mean I know 'they're not real', but for a PG rated Disney movie seeing people get dismembered and stuff was kind of shocking.

People concerned about it being a 'sequel' are doing it wrong. Don't go for the story.