Nemesis may not be great, but I enjoyed it, and held up against the dismal Generations and Insurrection, and the hugely over-rated First Contact it does not compare at all badly.
I just finished watching the Next Generation films, and really the only film that holds up particularly well in terms of story is First Contact.
Generations as a concept is a great story, but when you realize that the entire premise of Generations and Kirk's return are predicated on Picard's inability to win a fist fight with a crazed scientist you begin to realize how silly the whole thing is.
Insurrection to me is the worst Trek movie ever because it is insufferably boring. It's really nothing more than a glorified 1 hour episode of TNG artificially inflated into a feature film... and it feels like it.
Finally Nemesis... ahhhh Nemesis, how much I love and loathe you. A lot of potential. Like a previous poster commented, it was like a potentially great movie which just needed a rewite. Lots of great ideas, but lots of missed opportunities as well.
My biggest beef was the introduction of B4; as soon as he appeared I turned to my wife in the theater and said, "I'll bet Data dies at the end." So any potential emotion I may have felt at the end of the film was diminished because I knew Data really wasn't "dead," B4 just needed to get his act together.
Yancy