At first I was going to say I wouldn't even know where to begin to fix NEM. But swapping Shinzon with Sela is a great place to start and it would have transformed that screenplay.I always felt that the TNG film series needed just enough tweaks to make them better films. For example, one of the more obvious missteps, IMO, was not including Sela in NEM. In fact, if the TNG film series were to end at NEM, Sela's inclusion (along with Wesley Crusher) would have served as a bookend of sorts. In fact, I would want to see Sela appear in all the films, either as a cameo or a full-blown inclusion in the plot (Sela being rescued at the Romulan station in GEN; Sela secretly monitoring the Enterprise-E, just before the Enterprise-E warps to join the fight against the Borg; meeting Picard at the meet-and-greet function before being called away in INS). But, I digress.
So, what film or films within the TNG film series could use some tweaking, that might have made the film(s) better in your opinion?
I honestly don't have any significant problems with GEN or FC.