Oh there's so much to write...
I'll just stick to one thing--Shinzon.
He is ALL over the place.
He's dying, very soon. He needs Picard for some blood transfusion thing to survive. Shinzon will DIE without Picard's blood. Survival should be Job #1 for Shinzon. But it's not... in fact, he battles and otherwise endangers Picard's life and therefore his own.
He resents and hates the Romulans who imprisoned him in the mines. You'd think his beef would be against those who tormented him his whole life. But it's not.
Instead, he's got to destroy the Federation and wipe out the Earth. What's that all about? What's Shinzon's gripe against the Feds?
He's also got this great revolution to lead, his Reman brothers need to be freed from slavery and oppression. Add that to his to-do list.
Then he's got some personal grudge against Picard, where he can't be his own man unless Picard dies. So Picard must be destroyed for Shinzon to live, but first Picard must live to provide the transfusion to save Shinzon, then Picard can die.
Meanwhile, between dying and misplaced revenge motives and sweeping attacks against enemies and space battles, he finds time to mind-rape Troi, too. Is that just to add "evil" for the plot, or does Shinzon have other problems, too?
I don't know what the hell this guy is supposed to be about or what he needs to do or what's his plan or why.