It's boring to say this, but Spock's Brain is the worst, just because it has such a ridiculous B-Movie style premise for a show purporting to be hard-sci-fi.
A lot of the other episodes being listed here are really more a subjective dislike people may have with them, but they're not universally hated the way Spock's Brain is. For instance, Let That Be Your Last Battlefield, although ham-fisted, was really one of the most memorable episodes because of the stark visual imagery. To a sophisticated 40 something that I am now, it's childish, but I first saw it as a young kid, and it made an impact, and I also really wanted the rare Mego version of the aliens. The episode also has the destruct sequence that was recycled in Star Trek III.
There really isn't much to be said in defense of Spock's Brain other than that it has some new music written for it and it gave us the meme of "Brain, Brain, what is Brain?" If you completely removed it from Trek canon, it wouldn't have left a very deep hole.
A lot of the other episodes being listed here are really more a subjective dislike people may have with them, but they're not universally hated the way Spock's Brain is. For instance, Let That Be Your Last Battlefield, although ham-fisted, was really one of the most memorable episodes because of the stark visual imagery. To a sophisticated 40 something that I am now, it's childish, but I first saw it as a young kid, and it made an impact, and I also really wanted the rare Mego version of the aliens. The episode also has the destruct sequence that was recycled in Star Trek III.
There really isn't much to be said in defense of Spock's Brain other than that it has some new music written for it and it gave us the meme of "Brain, Brain, what is Brain?" If you completely removed it from Trek canon, it wouldn't have left a very deep hole.