I'm not sure if I would have wanted Sela to make a comeback, especially as the main villain. Tying the story to something from the series would have been nice though, maybe to the events of "Unification". Nemesis wasted the opportunity to explore Romulan society further and pose some interesting moral questions about the status of the Remans.
One thing I've never understood about the TNG films is why they tried to aim for a general audience by trying to turn Picard and company into cliche action heroes fighting some villain. TNG was never really done justice on the big screen because of this. The most financially successful Star Trek film before ST:09 was the Voyage Home which didn't even have a villain or a single action scene. TNG as a TV series was slow and cerebral, full of people sitting around conference tables and spouting expository dialogue or discussing weighty moral issues.
The TNG films were niche productions with modest budgets and the only real audience were Star Trek fans. They just had to keep making Paramount money. They weren't 100 million dollar spectacles like the JJ films that had enormous pressure to reach the widest audience possible.