For me, the biggest problem with NEM is that Shinzon's motivations are cloudy. We're told he self-identifies as a Reman and is a Reman nationalist... but out of nowhere, we discover that he hates Picard and wants to destroy Earth.
I mean, I guess I can understand the idea that he'd irrationally come to hate Picard. But the idea that he'd turn his genocidal rage against Earth instead of Romulus as the end of his life approaches just doesn't make sense. Romulus has been oppressing and terrorizing the Remans for centuries; as a Reman nationalist, Shinzon's goal should be to destroy all life on Romulus before he dies.
And the purple rubber outfit. Seriously, whose idea was that?
I was right there with you man. Shinzon's motivations should've been the genocidal destruction of Earth based on his background. Him hating Picard and wanting to destroy Earth makes sense though. It's not about justice or revenge for the Remans. It was about Shinzon destroying everything Picard stood for. Shinzon forging his own legacy and having Picard's erased along with Earth. Shinzon says this in the movie.
He didn't attack the Romulans because they supported his coup and he needed their support to fight the Federation.
Well, that's what I'm saying -- why is he so fixated on Picard, Earth, and the Federation? Why does he hate the longstanding enemies of the culture that brutally oppressed his adopted people and sent him to die in a mine? It makes no sense; as a Reman nationalist, his rage should be directed at the Romulans, not the Federation. Hell, even if he doesn't really care about the Remans, his rage should still
be directed at the Romulans, because they're the ones who enslaved him.
And "the Romulans" didn't support his coup. A faction of Romulan Imperial Fleet admirals supported it, but they were planning on using him as their puppet, and he knew it. Both sides were planning to betray the other.