X-Men is the Marvel super hero movie that finally made it and launched them on a series of quality film. It made it because it was great.
The good. Lots of super action. Nice displays of powers. Interesting story. A bit of intrigue. Well done bantering. A few odd references to the comic books for the fans. Great battles.
The actors. Hugh Jackman is perfect as the Wolverine, he's just missing a bit of bulk, but the attitude is there. Patrick Stewart is also right on as professor X. Ian McKellen makes a great super villain as Magneto. At that point James Marsden wasn't well known and this role is a little bit weak for him, he can perform better. Although Halle Berry was already a star, and she fits her role to perfection, it didn't stretch her acting talent at all. Anna Paquin plays the sweet Rogue with a good sense of dramatic flair.
The bad. The CG are starting to show. They're not too old yet, but we can see them on the edge. The story is pretty basic compared to the intrigue we can find in the comics. And Cyclops never was such a twerp in the books.
The ugly. Nothing.
The result. Great super hero entertainment.