Currently reading Star Trek #21: Uhura's Song by Janet Kagen. I'm really enjoying the world-building in this novel, but I'm getting a strong "Mary-Sue" vibe in the form of Evan Wilson...
A lot of people say that about her, but I think she's more in the vein of a type of story that was common in '60s and '70s television, an episode that was built around a character study of a featured guest star. Since anthologies were the epitome of classy drama in the '50s and '60s, even continuing shows aspired to an anthology flavor, and so they often had episodes that centered on the guest stars with the regulars in more of a supporting role. Wagon Train
, the series that Roddenberry presented to network execs as his model for Star Trek
, made that its trademark; most of its episodes were actually titled "The [Guest Character of the Week] Story." And you can see it to an extent in TOS episodes like "The Corbomite Maneuver" (largely Dave Bailey's story), "Mudd's Women" (mostly centered on Eve), "Charlie X," "Metamorphosis" (about Cochrane and the Companion), etc.
Since that type of guest-focused storytelling is less common these days, people tend to forget that a Mary Sue is not just a guest character who steals the attention from the leads -- it's a guest character who's badly written and doesn't deserve
to be the center of attention, a character who's asserted to be impossibly wonderful and worshipped by all the other characters but isn't actually interesting or smart or appealing at all. Evan Wilson is portrayed as a pretty gifted and fascinating person, but she's well-enough written to earn that portrayal, because she really is intriguing to the reader (IMHO, at least), not just alleged to be intriguing to the other characters.