Vicious, it's not that it didn't stay tue to the comics, neither did the other two. The problem is thatr the other two films tried to stay true to the essence of X-men, without following the comics scene for scene, where as this film was just a bad excuse to make money from a franchise. At least you can watch the other films and enjoy them as good films if you are an X-men fan or not, but this film was just terrible by all standards, it was like a bad fanfic.
I'm comparing this film to the previous ones, and that is where it falls short. Singer should have never left....at least Superman might be good....
This film was doomed from early on, first Singer left, then they went through several director/script changes, then they decided not to include Alan Cumming/Nightcrawler, then Singer took the actor for Cyclops to play a part in Superman so he only had limited time to film X3, so then the script had to be changed again.
**********MASSIVE SPOILERS****************
Forgetting about the internal problems, let's just look at it as a film. Nightcrawler is gone for no reason, Cyclops dies in the 1st 10 mins, Jean is touted as being evil and all powerful, the focus of the film supposidly but does pretty much nothing in the film, just standing there until a strange act of randomness at the end. Adding Angel was pointless as he does nothing, Rogue didn't do anything. Kitty was a wasted opportunity and took up valuable screentime that could have been used on other characters. X getting killed was retarded and again random, none of the characters felt like "themselves" as they were set up in previous films and there were far too many random mutants who added nothing and took up screentime. Vinne Jones as Juggernaught was dumb and his helmet looked like it was made of tinfoil. About the only good thing was Beast, he was done well and was underused like most characters.
As for the plot it was so dumb on so many levels....a cure for mutants....riiiiight...in a handy quick action gun form, how convenient....
It had no direction, the characters didn't feel right, there were far too many characters most of which were pointless and the film could have done without. Too much time was wasted on setting up things that had no purpose or introducing useless characters to waste time in between the regurgitated plot lines taken from older X-men films but not done well and the overall amatuerish/fanfic fealing of the film in general. Essentially it was a sell out movie with no artistic merit or integrity with actors who only did it because they were under contract and the whole thing was designed for some quick cash for the studio while raping the X-men franchise. It was shit, end of story.