The movie had so many things wrong with it. It regurgitated a lot of the same worn out TNG tropes, like the not funny at all "comedic moments", and the cringe inducing conversations like "Romulan Ale should be illegal" "It IS illegal!". Yuck! All to try to milk comedy out of mocking the characters.
Also it promises us Romulans, and instead we get these vampire creatures right out of an Ed Wood movie.
Then the whole movie is dark (literally and figuratively). I wanted to scream "Damn it! turn on the goddamn lights!". The whole movie was depressing, particularly watching all the characters looks so worn out, tired and looking like they could give 2 fucks.
Then they kill off Data. You do not. kill. Data. You just don't do it!
It hadn't occurred to me before, but I think that maybe with the darker sets, the bit about the Romulan ale, and so on, they might have been trying to call back to Star Trek VI, since they had a pretty good idea it would be the last outing for this crew (self-fulfilling prophecy, that, but, yeah). The HUGE thing they missed is that VI still ended with some hope - we all already knew there was someone to continue the Enterprise's legacy. We had no such promise with Nemesis, so it felt more like an actual END than a hand-off. Especially with killing Data. None of the crew got killed off in VI, thankfully.
Nemesis had some really good stuff, though, particularly in the space combat scenes. And I even think Shinzon was a decent villain, if he had been handled a little better. But what KILLS this movie for me is B4 coming out of nowhere (Data *could* have been trying to create an offspring again, would have made more sense than some additional random prototype and sensors being able to detect it several systems away) and even more so, the entire Reman species coming out of nowhere
! Seems like something we'd have come across before in the history of Trek - novels, screen, etc - doncha think?!