Babylon 5 ruined this episode for me.
You see, before Babylon 5 the idea of having a vast conspiracy just come up and be resolved in one episode was the norm. Babylon 5 started to do this kind of plot over whole seasons, which added to the impact. For instance, in a more modern era there would have been a member of the main crew acting strangely for several episodes before this one who then turns out to be infected, for instance.[^1]
So what might have been a great episode at the time is just a good one now. But it’s doing things that we’ve never seen Star Trek do before, and it has some fantastic action scenes. Oh, and an exploding head.
Great Star Trek moment: the first time in any of the TV shows that the crew has gone to the surface of 24th (or 23rd) century Earth.
130 down, 607 to go.
[^1]: In actual fact, the show is actually being quite innovative in that there was actually a link to this in an earlier episode, which is a first for Star Trek.