An important note about Spock's Brain: if possible, you should watch with the original fx. At the very end, Kelley and Shatner perform a gag that the remastered edition omits, because it occurs during a film dissolve to the Enterprise. The remaster cuts away early to avoid the original fx in the dissolve. I missed it as a child but my father burst out laughing. He had to tell me what they did.
I have a little more to say on SB as well:
Much like "The Mark of Gideon" where they built a whole Enterprise mockup, "Spock's Brain" has an alien society doing something impractical that draws our heroes in.
• If you just need a humanoid brain, wouldn't your own planet be the place to get it? It's quicker, vastly cheaper, and a sure thing, compared to going out into the galaxy looking for one.
• If you go to all the trouble of mounting an interstellar space mission, what are your chances of running into an alien ship with a prime specimen like Spock on board? Seems more like an impossible dream than a sensible plan. Kara must have been heading for a specific solar system where she knows there are humanoids.
• If only a superior "brain from space" will do, then they should have preserved tissues from the old Controller and cloned him as needed. Or when they got the old one 10,000 years ago, they should have gotten some spares and kept them frozen for later use.
• It's not clear what Spock's brain could be doing in that box, that an electronic computer could not do.
I like "Spock's Brain" for its good points, but it also seems like a first-draft, wild-idea story that should have evolved into a more respectable plot about visiting Sigma Draconis, with no brain stealing involved. Who knows what it could have been, if more work had been put into the plot.