Shelby's criticism of Riker in TBOBW was entirely valid, much as it rankled fans to hear it. Riker had spent so long in Picard's shadow that he had given up any hint of ambition and had forgotten how to command.
His ambition was the Enterprise. I'm sure he took the job because he hoped one day he would move from First Officer to Captain. It wasn't his fault that Picard was healthy and refused to die or retire.
That's a problem with the movies. He's been second for about twenty years just to keep the status quo of the show. After Generations, Picard should have considered retirement. By the end of Insurrection, he should have done it and give up the ship for Riker. That would have been a good change for him too because, next to Riker, he didn't grow as a character either:
Worf became Chief of Security (S2)
Geordi became Chief Engineer (S2)
Troi took her test to be a Bridge Officer (S7)
Data got his emotions chip (GEN)
Beverly was named chief of Starfleet med for one year (S2), so her rank is as much as she can be without being an admiral.
O'Brian got married, had a child, and was transfered to DS9 (S4/5)
Ro became lieutenant (S7)
Even Wesley finally went to Starfleet, despite he later abandoned it. It was still a change for him.
Meanwhile, Riker has been just Number One for two decades and it's kinda sad he never got his one ambition: being the Captain of the Enterprise (aside from TBOBW).
Maybe Nemesis should have started with Riker being the Captain after Picard decided to take a sabbatical with that Ba'ku woman and later returns to help them with the Romulans as a diplomat. It would also put in perspective how his life changed after losing his family and he's considering having a family, something set up since Generations.