Although I've been a hard core sci-fi fan since grade school, I've never found much appeal in any of the Star Trek franchises. Rodenberry liked to preach too much, and the later series seemed totally bland and had some of the worst production designs I've ever seen.
(So what's with the Klingons, anyway? In the original series they appeared human, but beginning with the first movie their heads turned into turtle shells or something. Same with the Romulans. Somehow they morphed into Neanderthals with jutting brow ridges instead of the Vulcan genetic stock or whatever they were supposed to have been. Was any reasonable explanation ever given for those drastic changes?)
You want good sci-fi on television, watch Firefly reruns. The scripts sometimes overcooked the wild west scenario, but the acting was good and the overall look was believable.
that bit with the Klingons was explained in a later series. I think it was Worf who stated that was a dark period in Klingon history, during a brief reference to the difference in appearance in the episode where DS9 went back in time to the tribble episode of the original series.
The gist of it is, the Klingons wanted to find out more about the humans, so they surgically altered some of their warriors to "blend" in with the Federation. Later generations did their best to not remember that "dark period" of shame in the Klingon history, as it used subterfuge, rather than ordinary brute force to infiltrate the enemy.
That is what I remember of the explanation, for what it's worth, and somebody out there may have more accurate info.
As for whether or not I like the original series, TNG, Voyager or DS9 best, I like them all. And I was particularly hopeful for the Star Trek Enterprise with Scott Bakula, but unfortunately, that got cancelled. It had a lot of promise, had they put a few more connections to the original series, it may have kept more of their audience, but however...
No matter the opinions of its detractors, Star Trek did have a lot to say about societal conditions and stupidities. It had validity to the society of the time.
Battlestar Galactica has validity to the society of this decade, and I am sure in 30 years or so people will be talking about how cheesy it was, etc.
The fact that we are all talking about Star Trek 32 years after its debut says something. That just about everybody on the planet with tv access recognizes Star Trek also says something for it. No snarky inserts as to exactly WHAT that is that it says, are allowed