Shinzon wanting to destroy Earth didn't make much sense to me either. Its a planet he's never been to and done nothing to him, or was he going to threaten to kill everyone on the planet unless Picard handed himself over to Shinzon?
His real gripe was with Romulous, but all he did there was kill the senators and seize control, what about the rest of the population? I find it hard to believe the Romulan people in general and the vast majority of the military would just accept it without any kind of opposition!
I like Tom Hardy, but I'd have preferred to see James Marsters in the role--but even better would have been Patrick Stewart with some X-Men 3 CGI to make him look younger