They didn't follow the original stories from the comics or previous films?
If it's the latter, I disagree, since it pretty much connected with the original trilogy (especially Erik and Xavier's history); with the exception of maybe a few minor things (since I THINK Shaw appeared in X-2, except as "Dr. Shaw"; not sure if it was the actual Sebastian Shaw). If it's the former, then well, no other comic-book film adaptation every follows what's in the comics 100%.
I not only thought it was the best X-Men film so far, but quite possibly the best film of the year so far. ("Source Code" and "Rango" being close behind). Every single aspect of the film was beautifully crafted (superb acting, intelligent dialogue, perfect flow of the story, awesome special effects, great musical score, appropriate comic relief), and I even felt way more emotion than all the previous X-Men films combined. (my eyes literally watered in one or two scenes, lol.)
But I guess we all feel differently about art, and that's what makes it beautiful.
....I personally hope this is the start of a new trilogy; as long as Matthew Vaughn remains the Director.