X Men: The Last Stand is definitely the most controversial film in the franchise, and with good reason. No doubt it's the weakest film of the trilogy. The list of complaints is long, from major characters being killed off too quickly and too early, an overabundance of characters with inadequate screen time, it's inaccuracy to the comics' timeline, and the many mutants with ridiculously lame powers, etc.
And yet, the film is not a failure. It's a well paced, well visioned, and quite epic conclusion that follows the trilogy's two main plotlines: the first being the battle between Magneto and Xavier, and the second being the political debate for mutant equality. Finally, the government has developed a "cure" for the mutant gene, and that sets off Magneto in a furious rage. What better way to start a grand battle between mutants, humans, and the X-Men.
Brett Ratner steps into the director's chair as a hired gun, and maintains the tone and mood of the previous two films. He manages to maintain a brisk pace and juggles the many handfuls of subplots as good as anyone could with a story this convoluted. Of course the film feels rushed at times, and with a cast this large, one can only see the mistreatment of certain characters a result of scheduling conflicts and actor availability. But all in all, X3 works. It may not be the perfect conclusion to the trilogy Bryan Singer may have visioned, but it's a competent one. At least the studio didn't fuck this one up too much.