Originally my biggest issue was Data dying and the inclusion of B4 and that was one of the reasons I didn't bother to see the film when it first came out. When I first watched it, I wasn't as mad since they make it fairly obvious that B4 is slowly turning into Data with his memory engrams. However, it basically makes the emotional impact of Data's death pretty much pointless and a ripoff of TWOK's ending.
In TWOK, it was pretty clear that the movie intended for Spock to stay dead (with maybe a string of copout to be used just in case). But TWOK ended as hopeful as it could possibly end, considering the subject matter.
Nemesis on the other hand, ended horribly depressing, emphasizing particularly that Data's death was tragic, and took a toll on all his friends.
There is no effort to give us a hopeful ending at all except for the very lame scene of B4 whistling Blue Skies (We know B4 is basically a primitive version of Data hardware wise, how could he ever become Data again without some intervention to upgrade his positronic nets, or whatever)
Anyway, bottom line, even if B4 was an acceptable cop out to revive Data, as far as the movie is concerned (to all his friends) the entire adventure was a horrible defeat and the loss of their friend permanent, which equals to a horribly depressing feeling on with the movie is content to leave that way.
I wanted to watch the TNG crew have one last victory, but the movie felt like I watched their permanent defeat.