I'm in the process of rewatching--slowly, through Netflix rentals--Star Trek Voyager. I've watched Star Trek Voyager over the years but never straight through so there are a number of episodes, especially in the first two years, that I've never seen. I quite like it, although it improves immensely after the first season. Voyager produced some of the greatest two-parters of all time. And they supplied the single best Star Trek couple ever: Paris and B'Elanna.
But to go back to the beginning. My thoughts on them all.
Star Trek: Original: My favorite aspect of Original, like many people's, is the Kirk, Spock, McCoy exchanges. There are also various episodes that are so well done in terms of script, camera work, plotting, etc. that they are classics in their own right. I don't include "Trouble with Tribbles," a great episode, since it isn't as tightly written as, for instance, "The City on the Edge of Forever" and "Amok Time." The latter two are almost seamless is their action/dialog/theme.
And I read Star Trek Original novels--well, really I only read Diane Duane (Spock's World), although I like The Vulcan Academy Murders by Jean Lorrah. Both authors, women, depict McCoy, Kirk and Spock the way I think they should be depicted.
Star Trek Next: Generation: Well, it's a little 80s and little trite and little too squeaky clean humans and a little silly, but it's also a ton of fun. I'm a fan of Data and I like Picard and Geordi and Worf; I like Riker, and even Troi doesn't annoy me as much as she used to. ("Captain, I feel their anger." "Yes, Troi, I picked up on that; they are shooting at us.") I think my single favorite episode is "Data's Day" although I like just about every episode Q shows up in as well. I can't point to any episode that I would call classic; however, there are classic performances. In the episode where Picard performs a mind-meld with Sarek, Patrick Stewart does an amazing job. (It's a good episode in and of itself.) The episode where Data creates a daughter is close to classic.
Star Trek: Deep Space Nine: Not everybody's favorite, and I admit that I gave up before it got into the whole Babylon 5 soap opera thing (if I haven't mentioned before how much I dislike being forced to watch a show week after week, I'll mention it here: I hate being forced to watch a show week after week. Give me single story episodes, and I'm happy. But give me cliff hangers, and I turn off the TV set). But I quite liked the set-up of Deep Space Nine. I thought it complicated the Star Trek universe. The Klingons were scary and mean; the Cardassians were evil and ambiguous; the Bajorans had heavy duty political problems and the Federation seemed on the verge of toppling over from bureaucracy. And the space station was always breaking down. All together, it was a far more complex set-up than I think the Star Trek universe could really handle. (They figured out the solution with Voyager). In his excellent Nitpicker's Guide, Phil Farrand (who didn't much like Deep Space Nine at first) expounds on some of the weaknesses--the inconsistent religious themes, for one, and the "we're on the edge of the universe/no, we're in the middle of Federation space" locale problem--but all in all, I thought Star Trek did as well as can be expected with such a complicated political/religious setting.
There are some definite notables:
Jake Sisko actually looks like a real kid. Instead of being wonder child, he behaves like that you would expect a reasonably bright son of a captain to behave.
The Ferengis are great, and Armin Shimerman deserves super kudos for his portrayal of Quark (and for the principal on Buffy). As Quark, he is a morally ambiguous character who still happens to have a basic moral center that, sometimes, seems lacking in the more noble Star Trek officers. My favorite Quark scene is when Odo trashes his apartment, and Quark comes to check on him under the pretext of making a complaint. It's nicely done.
The excellent Andrew Robinson as the other morally ambiguous character, Garak (one of my favorite episodes is "The Wire").
The evil but yet again ambiguous Gul Dukat.
All in all I think some of the most complex episodes ("Duet") can be found on Deep Space Nine.
Star Trek: Voyager: Voyager is a synthesis of Deep Space Nine with the usual Star Trek pattern. That is, you've got to get these people out in space, you've got to give them complicated problems to overcome, and you've got to get them away from the bureacrats who kill all the exciting episodes before they even start. You can't have captains disobeying direct orders every episode; it gets a tad unbelievable. So you take a ship, put it in the Delta quadrant, but give it a captain who believes, Shackleton-like, that the only way to survive is to maintain Star Trek discipline and who is aided in this by people who have all been trained at the Academy, even if they later went off the rails (Paris, B'Elanna, Chakotay). The result is episodes that attempt the complexity of Deep Space Nine without the attendant problems of having to maintain a consistent world (i.e. Bajor). I mean, after all, they can always move on. As I've mentioned, the two-part episodes are some of the best TV movies I've ever seen. With some of the shorter episodes, you feel that the writers came up with a very cool idea, got it going and then, oops, got to wrap it up, give me easy plot solution #6.
And I like Janeway. I didn't at first, but I think she is a nice contrast to the overly pugilistic Kirk and the underly confrontational Picard. At first, there was a bit too much "we have to make her tough but feminine" (which dissolved into motherliness) stuff. But Kate Mulgrew manages to pull it off. I was very happy when they got rid of the bun though.
And that's it. I can't comment on Enterprise. Despite the excellent Scott Bakula who I still admire from Quantum Leap days, I could never get into Enterprise. I loved the opening credits/music, but I just couldn't connect with any of the characters, and then when I went back to try again, they were doing some ahhhhh Babylon 5 thing where you had no idea what was occuring unless you'd watched the last six episodes. It was also less of a family ship, which would make sense, but that's one thing I like about the others: society in microcosm moving through space. Of course, Original didn't have families on board either, but they had the terrific trio, including that man from Vulcan. Actually, the two men from Vulcan; don't forget the adorable Mark Lenard. And Original reached the status of myth, after all. Not the easiest thing to live up to. (Let's just ignore the existence of "Spock's Brain" shall we?)
I have been, and always shall be, your friend. Spock to Kirk, Wrath of Khan.