I saw this movie, and I'm kind of with other people on this one. The effects were breathtaking, and Johnny was in good acting form.
My main problem with this movie is the premise. This movie was clearly made to capitalize on the 2012 scare, and in a way it really downgrades it. The movie really has nothing to do with the 2012 phenomenon, at least in the ideas of how the world is going to come to an end. Sure there is a reference to the Mesoamerican Calender, and if I remember there is shots of wide mass suicides to escape the apocalypse (correct me if I'm wrong, it's been a bit since I saw it), but that's about it. The end of the world is caused by a massive solar flare in the movie, but the main theories in real life involve the planets aligning, the reversal of the North and South Pole, and a black hole. I don't remember any of these being touched upon in the movie.
Overall, I think this movie is ok. It has good effects and acting, but not enough research was really put into the actual 2012 theories in my opinion. If this movie were given a different title, then it would fit better. If people go to see a movie about 2012, I would hope they would expect to see a bit more connection to the real life theories than simply the day it happens.