The super-powered human comes a bit too fast on the heels of WNMhgb but I like this episode. The Rec Deck scene is fun, Charlie is both creepy, dangerous, and sympathetic - where is the ship's counselor when they actually need one for a change? :P
The special effects in the episode are some of my strongest early memories of Trek. Uhura gets a fun scene and it is probably Rand's meatiest episode, although I wish they had credited the woman (or pretty much any woman in TOS) with a bit more common sense.