I saw that Adam posted about this movie. While I agree with most things that he said, I have one big difference: I absolutely would categorize this as a first class movie.
I think at this point, most know the plot of the movie so I will just skip those details. This movie was quite brilliant in it's connection to American history and in making the mutants more "human". I felt like this may have been the best x-movie to make that connection with these characters as opposed to just super-powered beings who want to fit in. There's a scene where all the new recruits/students sit around trying to pick code names now that they technically work for the CIA. As they are all still teenagers and/or young 20-somethings, this could have easily been a botched effort, coming out more like a Twilight scene than anything. Vaughn crafted it perfectly. These are how kids would talk in this situation. This is how people would react. This is the most "human" these "mutants" have been portrayed and a huge portion of that falls on the acting.
James McAvoy and Michael Fassbender were perfect as Xavier and Erik, with Fassbender probably turning in the best performance. Kevin Bacon also stood out, as I have never been a fan of his. I can name the movies of his I have seen on one hand and still be able to eat dinner with it. I found him to have just the right amount of villain cliche mixed with ruthless, world-dominating evil. Worst out of the bunch for me was Jennifer Lawrence and she wasn't even bad. I found her character (much like that of Emma Frost) just a bit underdeveloped. There were there and they were given parts but they didn't feel like they were anything too important. But I even liked them. It was a very well-rounded cast for me and I can't think of any other actors who would have done better (admittedly, I have not put much though into either).
Overall, I was quite amazed by this movie. With such low expectations due to Last Stand and Wolverine, I freely admit to being blown away. I put it second in the x-franchise to only X2 and I'm willing to let that set in and change if need. Once again, the comic movies of the summer are amazing and I can only imagine what Lantern and Cap are gonna do for me.