This is definitely a mood-lightener after all the serious sci-fi which has gone before. It's pretty fluffy stuff, long on mysterious happenings, fist fights, and visual non-sequitors, and essentially devoid of character development (though not of character revelation). Its purpose is really a change of pace, and it provides that rather nicely.
Sturgeon's script feels a bit like a patchwork job. While it is quite imaginative, and very much gets the tone of the characters (despite fixing McCoy up with an unlikely yeoman), the structure is such that it allows skipping and jumping around seemingly at random between the various crewmembers' experiences. There is no narrative to speak of, just a series of vignettes used to illustrate (and eventually escalate, though not deepen) the mystery. When McCoy is skewered, we learn that the visions can be hazardous, but we've really known that all along -- just not the degree. In fact, no new information is added after the intial unexplained visions.
When the answer is finally revealed, it's almost a disappointment. And it qualifies as a quick fix because of the rapid change from desperation to complete relief and laughter -- without any effort on the part of our heroes. They do not solve the mystery, the solution is simply handed to them in their darkest hour. The episode might have been a bit more robust if our heroes figured things out earlier and then went around trying to control their thoughts and rescuing each other from the various perils of their own creation while searching for a caretaker/control mechanism (perhaps even conjuring a faux caretaker at some point by simply thinking about it).
The opening scenes aboard ship set the stage nicely, including a clever turn by Spock to trick Kirk into going ashore. The closing scene, however, is a misfire which once again ends an episode in forced laughter at an inexplicable joke. Coon's desire for light-hearted moments is admirable, but it's always best if such things develop organically. Forcing them, like this, usually doesn't end well.
The location shooting is quite beautiful, and the various visions are neatly realized through inexpensive costuming (rabbit, Alice, samurai, Don Juan), cameo guest (Finnegan, Ruth), or stock footage (birds, planes, tiger). With only scant optical effects (standard planet orbit shots, two beam-downs), this has to have been both a money- and time-saver (although the cost in distressed uniforms must be considered).
None of the guests has a big enough role to be of any substance. Emily Banks as yeoman-of-the-week Barrows fits the standard mold: leggy and prone to fits of hysterical crying (which she does twice). Baldavin returns in a cameo of Angela which, since it aired in the week immediately following "Balance of Terror," raises questions about her dedication to her fallen fiance. For the record, she does get killed by the strafing planes, then resurrected with McCoy. The short scene which would have cleared this up is in the script, but didn't make the final cut.
Gerald Fried provides his first Trek score, which is quite lovely and contains a little in-joke riff on the main title theme which would become standard fare for lighter moments as the season wore on. Theiss turns in two truly odd costumes for McCoy's girls, and two lovely gowns (Ruth and Barrows).
The episode is satisfying as pure entertainment. It does not aspire to any message or great character insight, and definitely gets points for staying within its prescribed scope. Numerous details (if you choose to look) are confusing and/or out of place. But it is an inoffensive action/adventure plot which is fun to watch and always entertaining. And it can claim one thing that some of the other pure action episodes cannot: It is never dumb.
Rating: Middle-Upper (3)