Saw it in 2D, even though I missed seeing Part 1, part 2 was easy to get the gist of what was happening. I had seen the others though, so that helped
Just wait till the new one comes to DVD, then watch them all, they are worth it once you get passed the first few movies(I saw the first one years ago and was turned off it because of how childish it seemed to me. After seeing the other, darker films, was getting good)