I watched the '90s cartoon as a kid, but never read any of the comics. So from my point of view:
X-Men was an entertaining effort with some shortcomings.
X2 was all kinds of awesome.
X-Men: The Last Stand had two strong ideas that were short changed because they tried to tackle both of them in one movie (and the writing just wasn't very good to begin with anyway), in addition to underwhelming execution from all creative parties involved. Pedestrian would be a fair term to describe it.
X-Men Origins: Wolverine was just one giant mess with lots of aimless mayhem, a distracting parade of cameos and one of the worst movie titles to boot.
Looking forward to The Wolverine because of the creative team involved and the fact that it's not joined at the hip with X-Men Origins: Wolverine.