Sorry that should've read " Shinzon's motivations should've been the genocidal destruction of Romulus based on his background." I edited to reflect it. Well Shinzon says the echo triumphing over the voice was a goal for him. Legitimizing his existence by destroying Picard. Forging his own legacy and erasing everything Picard stood for. If Earth and the Federation were destroyed then everything Picard did, all the treaties, discoveries and battles he won become annulled since no one will remember him.
Couldn't Shinzon just as easily eclipsed Picard by destroying Romulus? The Federation's greatest enemy, wouldn't that have made his life more consequential, in his eyes?
I can get the whole one upping Picard thing that Shinzon says he wants to do, but it just felt a bit too overdone, hackneyed, convoluted or something. It felt like they had to take extra steps that they really didn't need to, to make Shiznon hate the Federation. It made more sense to me that Shinzon would hate the Romulans and want to eradicate them.
If that had been the case, we could've had Picard and company willing to sacrifice all to save Romulus, a reversal of what Donatra did, and that could've been a major moment in Federation-Romulan relations, on par with the events in Star Trek 6. Instead we got another tired Earth is in peril story.
I also disagree with what Christopher said early on about Shinzon and Picard's strong relationship. I think Khan and Kirk worked far better as adversaries because of their history. Picard and Shinzon had no history, so we could never get a great moment like when Khan first appears on the Enterprise viewscreen in Star Trek 2.