I'm very tired of people looking at plot elements that aren't totally explained on-camera, and assuming them to be "stupid" plot holes. We shouldn't need all the information spoon-fed to us. A lot of the aspects that people are complaining about, which seem to ruin the episode for them, are the most interesting parts, because they raise questions and lead you to try to figure out the answers yourself-- or at least that's how it's supposed to work.
"Spock's Brain" is like most of season three, the result of a talented, dedicated team making ST, at odds with a network that seems to have looked at ST and science fiction as childish trash, that wanted to play up that supposed childish trashiness for big ratings from SF viewers, whom they assumed to be idiots. F. Frieberger I see as their stooge or representative. The fact that the rest of those working on ST managed to keep the quality as high as they did is remarkable. What these efforts seemed mostly to consist of, though, was doing emergency CPR on bad story ideas and scripts that they didn't get to choose.
"Spock's Brain" is a combination of embarrassing elements and great moments. Not for one moment have I ever seen it as camp or comedy, as a child or now. I wonder whether if the costumes and speech of the Space Bimbos were less silly, the whole ep. might be seen differently. The scene in Sickbay is effective, dead serious, and jarring. The impossibility of the task added a strange sombre mood, since usually their challenges are right there in front of their faces. Spock's semi-dead body walking around while we imagine the empty skull we know is behind those dead eyes, that's a new sort of horror for ST. Best of all, DeForest's acting with the teacher and operation... As for Spock keeping his hair and chatting away afterward, guess what, this is supposed to be a distant future where there are almost inconceivable technological advances. This goes a bit too far, but they wouldn't be doing their jobs if the operation weren't jarring, surprising, and much further advanced than now.
I like the conference on the Bridge, the debate, and Uhura getting us back to the heart of the matter, asking WHY they'd want someone's brain... There are nice SF elements and implied backstory-- the idea of an organic brain being used to control all functions of a community as it does the body, the isolation and insanity of a fallen-apart civilization dealing with a new ice age, which may happen to us, and degenerating because of it...
"Spock's Brain" is actually one of the most interesting (and darkest and moodiest) s3 stories, but also with embarrassing bits. I choose not to let these ruin the story for me.