The dialogue was a joke. There were no moments of subtlety or character the way there were in the first two, everything was either "I am announcing something now!" or "I am confronting you now!"
Every time they had a scene with Kitty Pryde I was checking my watch again - they turned one of the most popular comic book characters into a complete cypher. Colossus looked ridiculous, more like the liquid Terminator from T2 than a man with belts of metal all over his body. Though Kelsey Grammer did an okay job, I think having him play Beast was the laziest casting choice so far this year ("Ooo, he's famous for playing someone smart on TV, let's have him play the smart X-Man!"). But the most egregious sin of all was that they did nothing with Phoenix. Absolutely nothing. For most of the movie she just stands around in the background, waiting for her big fight scene at the end. And what was up with the little-girl-from-The Ring makeup everytime she changed into Phoenix? And how come they never bothered using the Phoenix shape that used to manifest in the comic book? And how come no one noticed Nightcrawler wasn't there? Whatever. The whole thing was a mess.
There's a scene toward the end where the camera pans past a few tombstones, and I half expected one of them to read, Simpsons-like, "The X-Men Franchise". It's over.