To me the UXM title really went downhill from the #290's and didn't pick up again until around the Pop-topia storyarc. Basically all of the 300's were to me.
I know this is heresy as some people think of AoA as the second coming, but the art was too cartoonish/anime'ish and the writing was nothing to write home about.
The whole 400's were hit or miss, but I would say on the whole pretty good. As a matter of fact one of my favorite story lines of all time was in here, the "She Lies With Angels" story. Absolutely fabulous
It may be my age and the fact that these were out when I was a kid, but I love the stories from "The Mutant Massacre" all the way through the end of the Muir Island Saga were great. It had some of the best art ( Jim Lee, Fabian Nicezia, Marc Silvestri, etc...) and setup stories that still reverberate throughout the X-universe today.