I have to say Insurrection is better than Nemesis simply because we had Michael Pillar's touch, and he helped craft the Berman era Trek we all know and love, for the most part. As a feature film, it's largest criticism is that it felt like an episode of TNG, but this may not be the only criticism. It's really the only one I can think of, at the moment. Michael Pillar's original Heart of Darkness script/his "Fade to black" book published by his family(?) is definitely worth a look.
On the other hand, for Nemesis, you had some misfires and missed opportunities. You had John Logan taking script notes from Patrick Steward and Brent Spiner to the point that it was a film about Picard, Data, and the gang instead of the TNG crew. They utilized the Romulans without leaning on TNG connections (Sela, Tomalak, etc) You also had a director who was a great film editor but completely foreign to directing Trek, thinking Geordi LaForge is an alien, and treating him as such. Some of the cast felt a little alienated during filming, (maybe alienated isnt the right word choice, I'm pulling from memories formed 20+ years ago) and he just didn't seem to understand what makes Star Trek "Star Trek". If you listen to Stuart Baird's audio commentary, you can see where he was coming from making the film.
As a feature film, Nemesis has many criticisms - it was billed as "A Generation's final journey beginning" implying it was the beginning of the end, when it actuality, scenes were left on the cutting room floor and it was edited into an action hero movie with car chases, explosions, and another physical showdown between Picard the movie's Villain. (with third act special guest star Data). Ultimately, it was the end of the TNG films instead of setting us up for "The Search for Data" movie that we never had. That is, until Star Trek: Picard came along...
It's funny, when I was younger, I preferred Nemesis over Insurrection because it gave me all the things I liked in a kid in Star Trek and then some. (Space battles, pew pew, bridge viewscreen exploding, Picard's evil clone, etc.) Now that I am older and have seen TNG from beginning to end and all the other series and movies, my tastes flipped. But I can also safely say I never truly disliked either film.