A fantastic episode that really shows off good plots that Star Trek could come up with. Nimoy does a fantastic job as always.
If I had to find a problem with the episode it is a few minor nit picks. The creature that attacks little Spock uses Godzilla's exact roar. Guess it was on hand from the other animated series the studio was making.
The other is little Spock's voice actor. It is obvious he is been fed the lines a few words at a time. The words come out in an unsmooth manner. It is a minor problem, but it show that they used an actual kid for the role.