The only TNG movie that I struggle with is Nemesis, the rest I think are fine. However, if I could make changes...
Generations - It should've been the old cast and the new cast. I read about the problems they had scripting all those characters in but, dammit, work a bit harder, that's your job (I'm also aware that there were serious problems getting insurance for Kelley to perform which no amount of script doctoring would solve but this is all fantasy anyway so...). Also, the concept of Soran destroying worlds to get into the Nexus is fine but make the worlds more important. A rock in the middle of nowhere inhabited by a bunch of idiots who haven't even discovered Warp drive yet? Meh.
First Contact - It's pretty much perfect as it is, it would've been nice to see Lily kicking the Borg ass she looked capable of kicking perhaps? Tom Hanks would've increased the box office but James Cromwell is a finer actor.
Insurrection - I was with the Son'a and Admiral Dougherty all the way on this one. They were right, a few hundred people on a planet that they'd invaded (doing who knows what damage to the natural ecological development of it) against, well, everyone else in the universe? Hey, McCormick, pack your beige clothes and get the hell off the planet! Also, the bloody awful moment when Riker takes manual control of the Enterprise using that bloody awful Quickshot II joystick was bloody awful.
Nemesis - There is a good movie within Nemesis but, sadly, it is a good illustration of the criticism that people often level at all of the TNG films in that it comes across as an extended episode. Tom Hardy today would have made a ferocious villain but back then my Grandmother could've taken him down. So a better villain was required. Also, rather than waste all that time faffing about driving in the desert, why not fill the running time with an example of what the Scimitar and it's weapon could do to a planet in the same way we saw the Death Star destroy Alderaan? Also, someone should've been killed and that someone should've been Picard. I get that they were still hopeful of another movie but Data not-really-dying was a real cop-out. And it could have been done, look at the Wrath Of Khan, Spock died, we all felt it, and yet they scripted their way out it when the need arose.