In case you forgot: Most of the crew is drunk and the Enterprise is spiraling towards a fiery oblivion.
Watching much of the expendable crew go a little wacky is good for a few giggles; this episode may be Sulu's shining moment. (The dude is ripped!) So is watching the deadpan Power Trio try to manage a crew full of drunks. Literally, they're drunks. McCoy figures out that something on the planet basically turns water into wine, including the water in the human body. Spock's emotional breakdown after he catches the condition from Nurse Chapel, where he reflects on the kind of life his human mother must lead on Vulcan, tugs on those heartstrings and plays them like a fiddle.
On a lighter note, the running gag about Riley's incessant singing of "Kathleen" is a nice touch, too, though again I ask: what does TOS have against the Irish? Also, I don't know about you, but having a few syringes of McCoy's Insta-Sober cure on hand would make life a lot better.
Spock's breakdown is solid character development with a good deal of emotional gravitas, but Kirk's is just awful. Something about his hidden feelings for Yeoman Rand doesn't really ring particularly in character, maybe because they're all mixed up in his feelings for the Enterprise.
Also, what's with the random bit of time travel at the end? It comes across as tacked-on episode filler, but since it's not singing space hippies, I'm not going to complain.