Designed and played badly.

Compared to the 1st and 2nd X-Men movie, in which each director Bryan Singer has performed all subsequent parts (X-Men 3, Wolverine, First Class, Wolverine 2) falling sharply. Bryan Singer still had a sense of how you could embed the partly exaggerated capabilities of each X-Men convincing in scenes. This is completely different in First Class. In some cases the figures just ask each other, "And what is your ability?" In order to have a reason to be able to show them at least once. In X-Men 1 & 2 which was quite different, there had still mostly feel "Yes, awesome, like this one ability is completely natural used in a single scene without it acts forced or constructed."
In addition, the actor's performance of almost all players is quite modest. Only Michael Fassbender as Magneto young (and partially Kevin Bacon) stands out, namely huge! Logically, there are his scenes that still bring a little entertainment and two stars in the film. James McAvoy on the other hand I have taken off his totally inappropriate played Professor at no time, from the cast of the remaining young X-Men to say nothing.
Fans who liked the first two X-Men for their parts compared to other superhero films something more profound characters and the clever staging of super powers, I therefore advise on First Class.