Last week I saw DS9: Homefront and TNG: Unification, and I had the same thoughts about Nemesis: a bigger scope would have helped. We never ever see a single glimpse of the huge machinery that would be involved in a real life event of this magnitude.
All we see is a dozen of senators getting killed and then it's "Ah well, there's a new guy.", and then it's all about Shinzon and the crew of the Enterprise. The outside world doesn't exist. No media, no public, no other politicians, no military, no diplomats involved, nothing.
It reduces these films and episodes to chamber plays.
Just imagine the same story applied to a real world scenario: Chinese government gets wiped out, and some guy takes charge, and secretly prepares a devastating attack while saying "We want peace!". Such a film would not have such a tiny scope on screen. If it did, it wouldn't feel realistic at all. In such a film, we would see at least a glimps of the machinery. Media coverage, people's reactions, a more realistic politically and military machinery, etc...
Even the tiniest things would have added to the scope, like a scene outside of the Romulan Senate. Picard and Shinzon not confering at a small table, but walking through a park, with lots of extras, and buildings, and stuff and shit. Picard being on Earth in San Francisco when he receives the order to go to Romulus, and Janeway, as an admiral, is shown to have a big crew working for her in the background in her offices. Shinzon making a public announcement that he's the Praetor now, intercut with shots of civilians and starfleet watching the broadcast. Stuff like that.