The character set-ups don't match the payoff and the entire story falls apart as a result.There are no more significant plot holes in Generations than there are in any other Trek movie, and actually LESS than in the other ones with time travel.
Kirk's setup: He can't stand a quiet retirement; what he really longs for is to be back in the action. If only there were some way to get what his heart truly wants.
Kirk's payoff: He's now in the Nexus, which gives him what he really wants, and what his heart truly desires is... a quiet retirement? Huh?
Picard's setup: He's pondering the life he sacrificed, the family he forsake, the fact that there will be no more Picards.
Picard's payoff: He gets a family in the Nexus, the life he never had. But he very quickly leaves it behind and goes off to convince Kirk to go back with him, to makes difference, to get back in the action... which is what we were told Kirk wanted at the beginning of the film and so shouldn't require convincing.
The way each character was set up, it should have been just the opposite. Each character was given the other character's payoff. It should have been Kirk trying to convince Picard to go back. Obviously, the writers want their main hero to take the active role, but then if that's the case the writers needed to rewrite the setups instead of changing gears in the middle of the script and writing a totally different story. You can get away with a lot of stupidity in movies as long as the payoff matches the setup.
The sad thing is that I feel "Generations" had the most potential of all the TNG films.
Well that's actually a much fairer criticism than the silly "plot holes" one. I guess I could see it as their "road not travelled" fantasies where each is based on doing something far different than the path they took was.
You're right though, that whereas Picard's fantasy is at least based on his mindset before he enters the Nexus, Kirk's is sort of out of nowhere, and it's the opposite of what he was thinking about before entering.