The actors chosen fit their parts extremely well, with Kevin Bacon making for an excellent villain, who is assuredly not a Nazi, despite many claims to the contrary. Magneto's slow decent from hero to villain is done excellently, with the fact that there is no real 'turning to the dark side' moment, as opposed to some other trilogy I know of. And that is what they're trying to do with this film, set up for a new trilogy, which if I know my superhero movies, will have a good second film and then all go to crap.
The characters are portrayed well, if differently from their comic book interpretations, another thing which tends to piss off fans, but you can tell by the way they're making this film that they were trying to appeal to a wider audience, not just the small group of diehards. The soundtrack was good, and fit the film well, and the background to the film, the Cuban missile crisis, was extremely well done, and gave some scope to what would otherwise just have been a personal story.
That's not to say the film was perfect, some of the cinematography was below par, shots lingering far too long, and some jokes which kind of fell flat. The passage of time was also really not shown, and what should have been months appeared to be a couple of days, maybe a week. Also the mutants they chose, were in general kind of terrible, I mean Banshee? Darwin? Riptide, the guy who creates tornadoes whose name is never mentioned in the film. These guys are no namers, the only really entertaining mutant, Emma Frost, gets shoved away in a holding cell for about half the film.
But overall it was a good film, and a good revitalization of the series, much need after the near travesty of Origins: Wolverine and 3. The action scenes were one of the highlights, and Magneto's scene in Argentina at the bar was one of the best curb stomp battles I have seen in a while. So go see it if you haven't, and if you don't like it, well as Wolverine says "fuck off".