It seems that you selected Nemisis as the movie for comparison because you figured that was your best bet at making the case that Star Trek V is not the worst Star Trek movie ever. I don't see any other reason that the two are equivalent. Star Trek V is directed by one of the stars, had a larger budget than the previous outing, and was following the franchise's most popular film. Nemisis was directed by a total outsider, and had a smaller budget than (and was released long after) Insurrection. So the only reason to grab Nemisis for a comparison is if you're really defensive about how the world views TFF.
I totally agree that Shinzon is unconvincing as a younger mirror to Picard, and that the scenes with just Shinzon and Picard are very dull. I also thinking the final scene with B4 ruined any dramatic momentum they had developed with Data's death. Also, I think that the TNG cast was looking pretty old. With the obvious age difference between Stewart and most of his crew, Riker and Troi's aging comes across much less forgivable than in the case of the TOS crew. Also, everyone pretty much agrees that Stuart Baird was not the answer as the director to save the series.
Having said all that, Nemisis is light years ahead of TFF in quality. Even though Baird loved changing camera shots every other second, there's an uninterrupted shot that lasts more than a minute near the end, as Riker says goodbye to Picard. I don't think that's the best scene in Nemisis, but I do think that one shot outshines any of the directing and acting in TFF. I agree that the scene of McCoy anguishing over his Dad's death was very good, but even there you're forced to swallow the concept that Sybok - without any explanation - is able to make McCoy vividly relive the scene again, this time with Sybok in it.
I don't know of any special effects shots in Nemisis that were noticable embarassments, and of course the only decent FX shots in TFF were shots they swiped from Star Trek III and Star Trek IV.
I think TFF is not only the worst entry in the Star Trek film series, but to find a fifth entry of any film franchise that was that bad, I think you have to go back to the Ma and Pa Kettle series.