A bit of a comic relief episode, this is a fine example of the character interplay that makes TOS successful. It's also shows the rich Star Trek universe, with space stations, political characters, space traders, alien enemies, and unusual and desirable (to a point) space creatures. The tribbles themselves are an interesting alien life form, at first glance bewildering to Dr. McCoy, of little practical use to Mr. Spock, threatening to the Klingons, and with an inexplicable life cycle. The episode looks forward to the future of the subsequent series (TNG/DS9/Voyager) in emphasizing political influence and intrigue over the typical episodic phaser displays and bravado, the bar fight excepted. As such it became a great foil for DS9's time-traveling return to K7, and to a lesser degree the animated series' "More Trouble with Tribbles." Silly or no, it's classic trek, and a very enjoyable episode.
Review of The Trouble with Tribbles
