The story is reminiscent of more classic trek - away mission, something goes wrong, and the crew have to fix it. There was a lot of classic science fantasy tropes in here - right from the start with the blood magic to open the prison up. When immortality was first mentioned, my immediate thought was that immortality would involve consciousness transfer into another being, and we kind of got that, but not from the immortal beings themselves and instead from others that snuck in through the gaps in between dimensions. I guess these creatures are some sort of lovecraftian indescribable horrors. Seeing how Pelia and Batel both reacted to them suggests there is some shared history amongst many of the species that now exist, and that they all know instinctively to fear them.
They killed off a named character (F for Gamble), which is surprising, but definitely raises the stakes for the rest of the show. I was really not expecting that, and getting such in your face gore (pardon the expression) was quite a lot to take in. The evil doesn't really seem quite well contained in the pattern buffer, and I hope the crew notice this pretty quickly. If it's messing with the computer system, if it can quantum phase itself around any barriers, it should be obvious fairly quickly something isn't right. And the pattern buffer has shown that it can't keep stuff stable forever without continually re-materialising it, which seems like a really bad idea, so that needs dealing with.
Amongst the characters, Spock really shines out here as the voice of reason. If they had listened to him in the first place this whole thing could have been avoided. While I get where the archaeologists amongst the team were coming from, they should have been overruled, and Spock's only flaw here was not putting his foot down. As security, La'an should have pushed behind him on this, and chapel shouldn't have let her desire to explore cloud her judgement.
On sets: Nothing beats a good quarry, love to see that. I really like the exterior and background visuals within the prison - reminds me of the videogame manifold garden (highly recommended if you like first person puzzlers). However, I did feel that the physicality of the room (or just floor) they were on made it very obvious it was a set. The background visuals felt detached from the area where the away team were standing and, backgrounds aside, was too bland for my liking. I think it is a pity we didn't get to explore more because some parts, especially the exterior and the life form they found, had a really cool design.
The directing was good. It was tense, it captured the confusion in the prison well. The chaos on the ship was exciting and felt like there was a risk of real damage. My only major nitpick was it made it very obvious when the evil was first making it's presence known. I don't know if this was an attempt to capture the fact that the evil was there all along and it could choose when to appear, or if it was just trying to signal to the audience "hey, right now something's not right", but I would have preferred if it had been more subtle and let us try to figure out what was going on.
Great episode. With an episode like that I can see why they wanted to add some extra comedy ones around it, but I hope there are more like this. Though I could do without the eye gore, in future.