Not bad and fairly entertaining with decent to good visual effects, but the characters for the most are bland and the plot was paint-by-numbers. I only saw this on standard Blu-ray with no 3D but still was impressed mainly because a lot of times filmmakers will make obvious attempts to capitalize on 3D and while there were a couple shots where objects were flying at the screen, it wasn't imposing or too obvious that it took me out of the movie.
Dwayne Johnson was a good replacement (or addition) though if he's not too careful, he might be typecast to fill in numerous already established franchises (see: Fast Five and the upcoming GI Joe sequel). Vanessa Hudgens looks hella fine and alright in the female lead while Josh Hutcherson, like Hudgens, serviceable in a role, like the rest, finds them primarily acting against a green screen.
***¼/*****, (B-, 6.7/10, 2.5/4)