Really great characters, with really great character development. The plot might seem fast at first but it falls into pace.
I have not read the comics, so I can not say how true it is to them. But I have the other films form the mains series (that would be excluding the spinoff X-Men Origins: Wolverine), and I can say by seeing them there is some nice bonuses in plot points in the film. Where they show how a character got to be who he is, for example. It is not necessary to see the other films though.