Catspaw? As an introductory episode? I would strongly advise against that, it's not at all typical of Star Trek and also, typically ranked near the bottom of ranking lists, I believe.
I don't like it. But I think that it could be perceived as more fast-paced and adventurish, which she says that he likes, and might be one of those episodes who most likely will be able to lure him into the world of Trek.
I can tell you that the first episodes of Trek I saw were those on The Best of TOS DVD (as a kid I only saw TNG and VOY (which I never learned to like) on TV):
1. The City on the Edge of Forever
2. The Trouble with Tribbles
3. Balance of Terror
4. Amok Time
Trouble With Tribbles, I've never liked nearly as much as most do, but, I do agree with the others in that list as great episodes.
Another really popular episode I've never cared a whole lot for is "The Giant Flying Terd" one, The Doomsday Machine
. However, I do like "The Space Hippie one" The Way to Eden
a great deal, which I think is fairly unpopular. So, yea, I see your point, but, I really can't see Catspaw
as being a good introduction epsiode to get someone interested in the Series, and if it does get them interested, I'm not sure it's typical enough of Trek to allow other episodes to be satisfactory, if more of that's what they're looking for
The point is that the episode hopefully will fulfill that which he is looking for, and at the same time make him want to look for something else, developing other needs, that consequently will be fulfilled by other Trek episodes.
After reading her descriptions of him, I think it's either that or The Man Trap. Of course, I still think the episodes listed in my original post would be the best recommendations for any newbie if he wants to grasp the essence of Star Trek, which I think neither The Man Trap or Catspaw epitomizes. There was another purpose with my latest, insidious suggestions.