So I rewatched this one tonight, and I'm not going to reiterate everything everyone has said about it already. On first watch, I did like this episode bc of it's horror elements as well as the advancing character arcs, and after rewatching and before grading it, I have a few points to make:
1) So once Gamble was attacked, Christine and La'an took him outside to be beamed up and then came back. The rest of the landing party was inside. So the only reason N'Jal was killed was because he tried to exit by himself? Okay. Got it. I'd actually missed that during my first bleary-eyed watch early Thursday morning. I kept thinking "how'd they get him out?!"
2) I liked that little look Christine gave La'an and then Spock when they were all talking about the "preservers" theory and La'an said "fascinating!" See, I like those little moments and... er, glances

And aww now when I see Gamble in all his fresh-faced innocence breathe "ancient astronauts!!!" my heart weeps a bit. About that, I really don't think we've seen the last of this character. Whether or not they follow up on the last scene, he's too good to let go. But what do I know? I'm just an OG Trekkie who's used to too many great guest characters meet their deaths never to be heard from again.
3) So when N'Jal speaks, he/she speaks in his language and Uhura translates, but when the landing party speak, he/she is able to understand them? I don't see Uhura translating to him. So I take it he either knows Standard, or the UT is translating one way. Okay... just checking here. I am not quite up on how the UT is supposed to work at this point in the Prime Timeline.
4) Gamble's injury/death happened right around 20mins in...
5) When I was first watching it, I remember thinking that when Dr. M'Benga was examining Gamble's fingers and they looked kinda dark blue/gray/black... that that's not a good thing that his extremities seem to have turned darker. I now realize that meant he had already died by that point. *shivers* the horror/horrific moments on this show were really, SNEAKILY well done.
6) Spock has read Alice in Wonderland... I now want to rewatch Shore Leave LOL.
7) How did an unbroken sentient sphere get into engineering? Who brought it aboard? I must have missed that part.
8) I understand a lot of folks did like the previous episode. I did not. THIS episode is precisely the reason why I did not like that one. To a writer like me, little things can mean a lot. This episode adds to the lore of TOS. It gets Spock back on his perceptive yet logical feet and able to establish a solid, tensile working bond with Christine; it shows why without Christine Chapel's ability to restrain Dr. Korby's innate curiosity for the unknown, he made such a life-changing error. And we now realize that Dr. M'Benga may have had an increasingly difficult emotional journey as the CMO aboard the Enterprise... something that may have led him on to a different path altogether. ALL that is meat & potatoes to an O Trekkie like me, and though I am still unsure as to whether SNW is Prime Timeline, as the series progresses, I am sure that this particular episode may well be considered part of the stream that seats SNW firmly inside the Prime Timeline.
8) As an OG Phile (original X-Files fan), I always loved the MOTWs (Monster-of-the-week) episodes more and gave them a lot of rewatches over the years. My Trek journey has been very different, but when Trek makes a true horror (and at times horrific) episode, I am there every step of the way.
Grade: 10