I thought it was alright. Kevin Bacon was the best thing in the movie (as expected) even if his character was underutilized a bit. He plays asshole characters so well (look at him in Sleepers if you haven't already).
They sure did pick some daft X-men to appear in this movie. I'd actually say that Magneto is the only X-men I actually dig. The rest are dumb. I also think within the Marvel universe that the X-men are kind of cheap in how they get their powers. While other Marvel characters have proper origin stories the X-men are just mutants and that's it. Bugs me a little.
I think the films problem is that it goes from being really serious (cuban missile crisis, nazi camps) to being really corny and silly in the blink of an eye. Set a theme for the movie and stick with it I say.
I'd say the film is still worth watching. Stands next to X2 as the best in the franchise.