First of all I really enjoyed this movie, it is definitely one the best CBM, up there with Batman Begins, Spider-Man 2 and X-Men 2, but not as good as The Dark Knight which hopefully the sequel to X-Men: First Class is.
I know that this movie wasn’t faithful by not using the original first class, but because this is a prequel of sorts and they are following the Bryan Singer film timeline and continuity they cannot use Cyclops, storm or Jean for obvious reasons (age). But I have a theory with what Fox might be doing with the original first class. Fans are saying that they didn’t use the original mutants, but when you think about it, in this film, Charles actually hasn’t opened the school yet as the mansion in this film isn’t actually a school yet, but because the CIA base was destroyed by an attack from Sebastian Shaw, the mansion at this point was just a place to go to train and stay. Also the mutants you see in this film aren’t actually his FIRST students (well they are a little) but more of a quick recruit army to stop Sebastian Shaw but helping them control their powers and training them along the way.
In the sequel or the third film when Charles actually opens the Mansion as a school, I think that Havok, Banshee and others will go off and do their own thing while Cyclops, Storm and Jean will be Charles’ first proper students at the school with Beast staying being the scientist of the team. This theory will also help continuity with when Charles in the first Bryan Singer X Men says to Wolverine that “Scott and Jean were one of my first students” implying that they were his first students when the school opened rather than his first quick recruit team with Banshee, Havok and others.
I agree that the film shouldn’t have been called first class as it is a little misleading and is a little of a slap in the face for fans. A title I would have preferred is something like X-Men: Genesis or X-Men Begins (Not X-Men Origins: Magneto as it is too reminiscent of X-Men Origins: Wolverine and we all want to forget that film, which this film also does with Emma Frost etc) and for the sequel something like X-Men: Evolution or X-Men: Revolution and then save X-Men: First Class for the third film as it would be more suited when Charles first opens the mansion as an actual school and Scott, Jean and Storm are his first proper students at the school and would be a better fit.