Well, the third X-Men movie is probably my least favorite of them all, but to its credit, it did have the most spectacular mutant superpower battles, and that's of course a huge part of the reason to see the movies in the first place. It was just sappier than the first two, with some really terrible lines.
Still worth seeing, I'd say. Plenty of Picard and Evil Gandalf and Halle Berry to go around. You're not going to see an X-Men movie and expect one of the great literary works of our time anyway.