X-Men First Class is a prequel to the popular X-Men series of films. It features many major characters in their youth (or at least younger than typically depicted) and is set in a world which could easily develop into the politically divided and complex world which these characters will come to inhabit in the future. We get to see a Professor X and Mystique befriend each other as children and watch their relationship grow. Professor X displays some hormonal and fittingly youthful behavior as a young man while Mystique struggles with how she fits into the world around her.
Magneto's story is arguably one of the most interesting aspects of the film. He goes from a young boy in a Nazi camp to a man poisoned by anger. He has arguably noble goals but is prone to making sudden decision without regard for how they might play out. This has dire consequences.
Kevin Bacon is brilliant as Sebastian Shaw. Shaw is the former Nazi and mutant who spent years torturing a young Magneto. He wants to wipe genetically typical humans off the face of the Earth and he will happily harm his fellow mutants in order to do so.
Overall the story is strong (perhaps a little less so than the other movies) and the characters are interesting. Wolverine's brief cameo is in my opinion one of the best parts of the movie. It has a lot of interesting contributions to the film canon and is well worth a watch. For the love of God avoid sudden death!!!