I loved the first X-Men movie and enjoyed the next two. Wolverine was a different story, but I found myself watching X-Men First Class with the same wonder as the first movie.
I did have one major quibble though. You know from the earlier movies that Professor X and Magneto are friends, despite their different views of the world. What you never see in those movies is a relationship between Professor X and Mystique. And yet, according to First Class, they grew up thinking of themselves as brother and sister. There aren’t even hints of this in the earlier movies.