This is one of those fairly rare episodes where I have no vestigal memory at all of what happens. I think that adds to the enjoyment of any given episode, although I think this episode was pretty good to start with.
Firstly, on the plot side it had an interesting concept (aliens from another galaxy!), and an interesting variation on the usual super-powerful opponents theme. The story gave plenty of opportunity for some fun scenes with Kirk, Spock, McCoy and Scotty.
And secondly, there’s a lot of geeky Star Trek stuff in here. There’s a reference back to the second pilot episode and the energy barrier, Kirk seduces women to save the day. And there’s also Scotty’s disturbing hidden alcoholism (well how else do you explain the massive quantity of liquor hidden in his quarters?). And there’s even a red shirt for good measure.
51 down, 686 to go.