X3 is an utter failure; it’s the worst of the X-Men films. Here's why: The Phoenix storyline is mishandled, and the script changes the personalities of important characters. It's strange to see Cyclops, Xavier, and Magneto acting so poorly. Halle Berry seemed to require more screen time, which results in her appearing frequently, but her character lacks development and sometimes delivers lines that go against what she previously stated. Rogue’s role has also become a disappointing, whiny subplot within an unnecessary love triangle, especially considering the original trilogy began with her as the focus. The film crams so many mutants onto the screen that some of their powers would be funny if this were a parody, but here they are treated completely seriously. This means every character feels one-dimensional because there isn’t enough time to develop them. It doesn't help that the movie carelessly eliminates or kills off roughly half the team from the previous two installments. Instead of being surprised, I found myself unsure who to support (with the exception of Wolverine). The film rushes through scenes just to get to the next action sequence; at only 93 minutes, there’s no opportunity to understand what's happening. Predictably, it ends with a scene designed to set up future installments and imply that everyone will regain their powers, which essentially makes the entire movie meaningless. The production budget was $215 million, but only about one-fourth of that is evident on screen. The special effects, green screen work, and makeup are noticeable and look awful. So, the film looks bad, tells its story badly, and treats its characters poorly. X3 is just plain bad.

Source on TMDB