The Romulans are very under used, and the new Reman guys are not explained very well or used. Come on, fans have wanted to see more of the Romulans as kick ass as bad guys for years, and when they had the chance they blew it. They could have had Denise Crosby return as the half Romulan Sela once more, and we could have seen her fate. But no...
The Remens felt like nothing more then space vampires to me. They sucked.
The B-4 Data twin thing was something done way better in the past with LORE, and I feel it would have been much better just to have had the great evil LORE come back. B-4 was foolish. They did not even talk about LORE in the move in regards to finding B-4, and that was strange to me. The Troy mind rape was not something that helped the story at all, and was something done much better in a past STNG episode. It was as if it was put into the film just to give Troy some extra screen time. The Picard clone did not look like Picard. It did not feel or act like it was a clone of him, so it did not work for me. Patrick Stewart should just have had a duel role. More Patrick Stewart is never a bad thing.
We get like zero character development in this movie. Ok, Riker and Troy do tie the knot, but we saw that coming for years. It would have been nice to show a development of Picard and the Doctor love relationship once and for all. At least that would have taken that story full circle. Star Trek Five had much better Character Development then Nemesis.
They knew this was going to be the last movie for this cast, and they just blew it.