Berman Trek was becoming stagnant. Your casual viewer wouldn't know Berman from a hole in the wall, yes. But they sure as hell knew that other sic-fi and fantasy fare such as LOTR and The Matrix were passing Trek by in style as well as substance. NEM looked old. NEM looked like it was made on the cheap. NEM's story was in no way innovative.
That's why it failed.
I agree with a lot of that. I remember feeling that the crew looked so old, tired, and bloated when I saw Nemesis in the theater. The whole affair just felt tired with even the reaction to Data's death being muted. Heck, even Riker's reaction to Troi's mind rape was a bit tame. He should've beamed over to the Scimitar and beat the stuffing out of Shinzon, or at least made the attempt. And if not him, Worf.
Even though I didn't think the Remans should've been included, or made so monstrous, I don't think they were the sole problem. I wish the Berman had had confidence that the Romulans were good enough to carry a film and that they were more multidimensional-potentially-than the Remans could be. That being said, I am finally glad that we got to see a subject species in the Romulan Empire. I got tired of seeing these 'empires' composed of just one species.
There was a sense of stagnation and it was evident in ENT too. Compared to BSG and LOST, plus many of the other genre shows of that time, it just didn't feel vital, it wasn't gripping, it rarely had you on the edge of your seat. ENT is better in retrospect than the first time around, but that doesn't mean much since I don't think it did enough of its job when it should've to hook in viewers. NEM didn't either.