Shinzon's motives were very confusing. He has such hostility and hatred for Picard, a man who has done nothing for him. He eradicates the Romulan Senate, but that's where his revenge against the people who created him and then dumped into a pit to rot ended. He should have been on a bigger rampage against the Romulan Empire, rather than Earth/UFP.
Then they should have dropped the whole "if you'd had my life you'd be just the same as me" and "I'm a mirror" crap. The nature-vs-nurture debate does not need a film made about it, especially not a Trek film.
Nemesis should have been the TNG crew's ST6, with them and the Romulans finally starting to make proper overtures towards peace.
Commander Austin Harris, First Officer, Deep Space Nine (by FltCpt. Bossco)
8.01 - Darkest Before Dawn
(Chapter 8 added, 12/09/2015)