Sadly, even though I had never seen this episode I immediately knew the predictable "twist" of the episode about a third of the way through. Then of course they allow the man they find on the planet to have free reign and wander everywhere on the ship, even though they really know nothing about him and he seems a bit nutty.
The effects aren't great or horrible and are essentially just film negatives superimposed with other pieces of film. It may have been neat in the 60s, but I suspect even then it wasn't exciting enough spend so much episode time on it when they could have been doing something more interesting like filling plot holes or developing characters.
This is one of the weakest episodes in the first season.