I thought the movie was brilliant. I mean people go on about the retconning of the story and the comics etc in all the movies (heck people do it with games too, remember the fuss about Halo Reach and the books?) all the time and to that I'm going to point out that even the comic books retconn the
out of each other. I mean seriously how many different Xmen comic lines are out there now? It's borderline ridiculous.
As a movie it was enjoyable, well filmed the casting was brilliant and the cameos within the movie were excellent. Especially
(SPOILER)Wolverine showing up and simply stating "go smurf yourself" (though the line needed "bub" on the end to truly fit with Wolverine's attitudes in life). I was cautious about the idea of McAvoy being Charles Xavier but you can definitely see how he went from the position he is in during the first class movie to the position he went to in the earlier Xmen movies. He portrays the role of young Xavier so very, very well the right amount of arrogance and over-confidence in his own abilities.
The inclusion of Havok was brilliant I know in the comics he's not meant to be older than Scott Summers but frankly when I first heard about the movie I believed they were going to go with the idea of Cyclops which is entirely what IMDB said in it's initial document about the movie. That would have been a mistake for sure, the idea that Havok is in however kinda sets up the whole situation for Havok to actually be portrayed as the father of Scott Summers (which consider the time line, the fact that the film is in the 60s is more than plausible).
The film does a good job of explaining why Wolverine was not present in it and at the same point lends itself to helping the credibility of all the previous Xmen movies including Wolverine to a degree though the inclusion of the ending of Wolverine showing Emma Frost as a child during the escape of the mutants from the Deadpool development center. Is a jarring conflict of information. Personally I prefer the idea of Emma Frost in First Class as it fits in better with the whole fact that until Jean Grey becomes Phoenix she's the most powerful threat to Xavier that he doesn't exactly know how to deal with.
Over all the film is a good movie, if you're a comic geek who is expecting the movies to be the exact same as the comics, get over it because they're not the same and frankly if the movies were the same as the comics or even the old cartoon series it wouldn't be as good because of that fact. And if you consider it as not being as good as the comics are then try viewing it as different. In other words try to watch the movies forgetting what you know. If you can't do that then simply don't watch the movies.
To be honest I would definitely like to see more Xmen movies from the same director, he's done a great job with it. I wouldn't even care if they considered this a reboot point and redone the entire Xmen Trilogy. So long as Hugh Jackman keeps his role as Wolverine.