For me, Trek went into convulsions the minute the producers said they were only going to do episodic format because arc-heavy series would have trouble appealing to the casual viewer. Now, I don't know about the US, but here in Blighty even soap operas have story arcs, yet the unwashed masses have no difficulty tuning in.
The next bad sign was the lack of character development on Voyager, not to mention the Magic Reset Button and "Technobabble is your Friend" philosophies. At this point a defibrillator was needed.
Then we got the Busty Borg Babe. Now, don't get me wrong - there's nothing wrong with casting an attractive woman. And, if she can act as well as Jeri Ryan can, there's even less wrong. But, c'mon! Like she wouldn't still be attractive if dressed normally instead of in a spandex bodysuit that pushes even the phrase "skin-tight"...
And now Enterprise. Don't even get me started. Shower scenes. Yet another busty but sexually unattainable science officer (Do you think Braga might have issues, here?). Rehashed plots (Ooh, look! The plot for the upcoming episode "Dawn" appears to be a retread of "Enemy Mine"!! Surprise!". The most popular character is the beagle for Pete's sake!!!
I look back at DS9 and the better episodes of TNG and wonder where it all went wrong...
"That might have been the biggest mistake of my life..."
"It is unlikely. I predict there is scope for even greater mistakes in the future given your obvious talent for them."
Vila and Orac, Blake's Seven