I've recently watched Nemesis again, and I am amazed how utterly boring it is, despite having more action scenes than the previous TNG films combined.
And I think I know the reason: the direction.
ALL dialoge scenes are characters sitting or standing around doing nothing but talking. And that in a very low key way. There is no energy whatsoever in the character's performances.
Here one example:
Try to imagine the exact same dialogue on the bridge. Imagine it with more energetic performances, a bit louder voices. Imagine it with camera motion, with the characters walking around a bit from viewscreen to the Captain's chair, etc...
What First Contact and Insurrection in comparison. See how Jonathan Frakes staged dialogue scenes. He gives the actors something to do while they are delivering lines. He keeps the camera in motion, he keeps the people in motion. He even keeps the background busy. That way - when dialogue performances are not enough to carry a scene - the action around the performance carries the scene.
Try to imagine all dialogue scenes in First Contact the way they are done in Nemesis, with everyone just standing around doing nothing but delivering their dialogue. Those films would suddenly fall apart.