I feel Nemesis gets judged overly harsh as it followed Insurrection which lost a lot of good will and quite frankly by that time Star Trek had gotten tired. While Enterprise was the nail in the coffin, you can blame the state of Star Trek on the people who conceived and crashed Voyager, so you can blame Star Treks demise on Janeway. Even Kate Mulgrew felt her character had gone insane and played her as such.
Nemesis was more of a Star Trek film that that latest crap from JJ Abrams, at least.
I liked Voyager all the way through. It had its problems, but was pretty consistent. Sure, the characters started out cheesy, but so did TNG. Really, the only issues I have with Voyager when looking back on it are twofold: Janeway knew everything. She was a jack-of-all-trades, instead of relying on her crew as other captains would have. Also, they kind of watered down the Borg by the end of the series. There were some pretty awesome Borg episodes, but they were practically declawed after so many loosing encounters with Voyager.
For me, I felt Star Trek started to slip towards the end of Deep Space Nine. I always felt that the characters and situations were a little dull on that series, but the last two or three seasons were ridiculously boring. Far-reaching war story arch? Switching out Dax at the last second? Going hogwild with Sisko's whacky cult status? Turning Dukat into Satan-incarnate? ...Yeah.
Likewise, I thought Enterprise was good until they again introduced a serialized war story. It immediately became boring at that point. I could complain about the inconsistencies in continuity, but the "temporal cold war" explains that away easily enough, I suppose.