I'm going to watch X2 again soon to be sure, but I really think this is the best X-Men movie. I was extremely skeptical of retelling this story, but it is done incredibly well. Surprisingly, the three characters who appear in as "adults" are all played be very talented young people here -- if you fear going to a movie where you're going to hate Magneto, Xavier, and Mystique, be afraid no more -- all three of those roles are incredibly well played.
TL;DR -- Go see this _now_, it's amazing.