Well, I've finally finished watching all of TOS for the first time, watching seasons 2 and 3 several weeks ago, and all 6 movies in the past week. I decided to skip the animated series for now.
Season 2
"Return to Tomorrow" - I loved Spock's evil smile and sarcastic remarks. It's just so out of character, it's a treat to see.
"The Changeling" - Enjoyable episode, and I see that this is expanded in one of the motion pictures.
"The Ultimate Computer" - Another one where the computer is defeated by a contradiction, still enjoyed this. This to me is one of the classic Star Trek cultural elements.
"Spectre of the Gun" - When Spock concludes that they are harmed by the guns merely because they believe they can be, and thus comes to believe that he cannot be harmed by them, he explains this to the other away team members. He says that they must be absolutely certain of this, and suggests that he do a Vulcan mind operation with them in order to give them this the same confidence he has. Why didn't he just have each of the members shoot him, so that each would see that it doesn't cause any harm firsthand? That would convince them all with certainty, and take less than a minute. It seems like the producers just wanted an opportunity to do some Vulcan voodoo.
Season 3
"Wink of an Eye" - Provides an interesting puzzle for them to solve. I like this kind of episode, with some kind of technological obstacle for them to overcome by cleverness.
"Whom Gods Destroy" - This is an example of the kind of episode that I find terrible, with a stereotypical madman or someone just wanting power over others. Good there aren't too many of these.
"Let That Be Your Last Battlefield" - Loved the scene with Spock and Kirk listening to one explaining how bring colored white on the right side and black on the other is so very different from the opposite. This is probably one of the best episodes, in having a clearly-defined subject and many powerful scenes.
"Return to Tomorrow" and "Is there in truth no beauty?" - It was fun to see Doctor Pulaski (Diana Muldaur) decades earlier as the science officer Ann Mulhall and Dr. Miranda Jones, respectively. Her voice/accent is so distinctive.
Movies
Star Trek 1: enjoyable to see things with high production values. Felt sort of like Star Wars (in a good way), but also 2001 in the way it was somewhat psychological.
Star Trek 2: I admit it, I wasn't looking forward to this movie at all. I didn't particularly like the Khan episode, and the title pretty much gives away what the movie is about. But wow, after 15 minutes of the movie, I was loving it! This was such a contrast to the first; here, once Khan gets on a ship and the Enterprise is going to stop him, you know where everything's headed, and in your mind you're putting it all together and imagining how it will end. For me, this really makes a movie enjoyable.
Star Trek 3: This one was pretty enjoyable too. I liked how Kirk and friends worked outside regulations on their rescue mission.
Star Trek 4: I like that they explored the same "palette" as on the show, here doing the obligatory travel-to-Earth episode. I have to admit, the humor in this movie really worked for me, even though I'm pretty picky when it comes to movie humor in an otherwise serious film. I couldn't stop laughing after the scene where Chekov was asking where to find the nuclear wessels. Just the way he was so clearly drawing bad attention, but oblivious, worked so well. The other one where the woman asks Kirk if they want to eat Italian, and Kirk and Spock do that "yes no... yes no... yes... yes" exchange, with Spock seeming to really not want Italian, also was great. I think the measured use of humor, without insulting the viewer's intelligence, is why it worked. Otherwise the movie is serious, so it doesn't detract (I'm hinting at my comments on Star Trek 5, as you can probably tell...).
Star Trek 5: Oh wow, what happened here? It started out interesting, with the guy having people open up about their deepest fears and hurts, but just went really bad. Someone tried to put way too much humor, and it was the kind you'd find in a movie like Idiocracy, not Star Trek. After seeing this, I was worried about whether I'd waste an hour+ watching the 6th movie.
Star Trek 6: A decent final movie centering on the original crew. It had lots of interesting elements, like the moon exploding and the huge ecological disaster, the Klingons' focus on military being their potential undoing, and relations between them. For a good part of the movie, I thought it would turn out to be Spock who was one of the two assassins, since near the beginning of the movie he was saying things that suggested he would be doing something later that would end his serving as a member of Starfleet. This movie felt a little overdone, as later movies involving TNG crew would be, having somehat involved conspiracy plots and twists. I tend to prefer a simpler plot.
Here's how I rank the movies relatively: 2, 4, 3, 6, 1, 5
It was a real treat to have so many movies to watch, now that I'm a fan of TOS in addition to TNG. The 2-3-4 trilogy was especially good, despite that they didn't plan on having one in advance. I've been really impressed with how well the film was restored in the DVD versions of the episodes and movies (redone effects aside).