The more I think about this episode the more impressed I get. There's so many small moments where they could have taken the easy, obvious choice and it would have been fine, and instead they were just a little more thoughtful and a little more creative and it shows.
They could have just had Pelia push a secret button to reveal her stash of alien tech, and that probably would have been fine. Instead they show her as this woman who's very smart and obviously immortal but otherwise...just a person living through history, which is so much better. Imagining the 250 years between the present and when she's one of the most famous engineers in the fleet is fun.
They could have had the Romulan agent just be a cold, ruthless assassin from the future who's here to get the job done, and that would have been fine. Instead she's this slightly unhinged woman, trapped out of time, stuck undercover on an alien world for thirty years on a mission that she's not sure exists anymore and I love the way she starts losing it at the end, that she just wants to kill this kid and be done with it.
They could have cast Khan as a hot 20 something available in the Toronto area and had him to a Ricardo Montalbán impression and give us a tense standoff, and I would have been annoyed at that, but it probably would have been fine. Instead they show us an actual child, and remind is that Khan was a horrifying monster, but he was created by a world with monsters of its own, monsters who built a child in a laboratory and raised him in a basement, and suddenly its a piece of implied context made explicit that I didn't even know I wanted.
And of course they could have just had Kirk agree to fix the timeline because its the right thing to do, or because he loves La`an, or because...honestly, because the plot has to happen, this is something that so many stories would just gloss over to keep the story moving. And instead we get one line, "Sam's alive?" and my heart jumped to my throat a little bit and immediately we understand why he's willing to go through with this.
I'm really really impressed with the writers on this episode.