I dunno what to think of this episode, because the vast majority of it was an utterly mundane (but serviceable) Trek "medical mystery hour" but some of the final 10 minutes or so are better than anything we saw in the first two episodes in terms of the use of themes and emotionally moving elements.
Once again, the episode keeps a close focus on a single character, with the POV character clearly Una, who even has framing log entries at the beginning and the end of the episode. Pike and Spock are stranded in a B plot specifically in order to give Una a chance to shine. This B-plot is largely useless plot mechanics, since the realization the two of them have about what happened to the Illyrian colonists is something which would be self-evident from the A-plot, but hey, sometimes you just structurally need these, like when Sisko just hangs in his office for three minutes.
Looking at it from a meta perspective, the writers played a very good bait/switch on us. We were all expecting that La'an would be the augment, and although she might have some fractional augment ancestry, that's clearly not salient. Instead Una is...and apparently an alien too? Or are the Illyrians (since it's the name of an ancient country in what's now Yugoslavia) some lost human colony? The played kinda fast/loose with whether Una was really an alien here, which I think is deliberate on the part of the showrunners. Whether Una is an alien or another type of human augment isn't important. What is important is that she's discriminated against, and has been living closeted to hide that ancestry and serve in Starfleet. While there's forward movement for her here, with several key crew members (Pike, M'Benga, Chapel, La'an) now knowing the truth about her, I love that in her closing monologue she notes there really is no closure, because a lifetime of insecurity about identity can't be overwritten because a few friends accept you for who you are - not when society as a whole does not. This is incredible allegorical storytelling - I just wish they didn't wait until the very end of the episode to get here, instead spending all the time with the magical light virus!
Other characters of course got some more time to shine here as well. La'an has a few layers of the onion peeled back, as was noted, we get to see a little more of Chapel (though she's still mostly a quippy cipher), and Hemmer comes more into focus. But the unexpected co-star is M'Benga, who unveils his deep dark secret - a dying daughter kept in the transporter buffer. This is manipulative as hell on the part of the showrunners, but as a father every time that Star Trek does these sort of things it gives me the feels - not just in fantastic episodes like The Visitor, but also in mediocre ones like Time's Orphan and Real Life. Babs is acting his heart out here as well, so this was a highlight of the episode, though I'm left wishing they did an entire episode about this instead.
The problem with the episode is aside from Una's character journey and the last-minute reveal regarding M'Benga's daughter everything else is mediocre as hell. This is a very tropey, TNG-like episode. The expository dialogue was quite clunky in places compared to the first two episodes, and holy hell was there a lot of technobabble here. Almost everything genuinely good happened in the third act, leaving the first two just...serviceable.
