I was really impressed with Moffat for this week's episode, which makes me feel as if he will do Capaldi justice by giving him even better scripts for his final episodes. This episode really intrigued me and distracted me so well from whatever's going on in the real world around me; I was immersed into the storyline.
The Vault reveal may feel a little underwhelming because it was obvious, but that's only because it was the only thing that actually made sense to be inside. And it was revealed halfway through the Series, so the Vault storyline is definitely not over, and it was clearly never about what is inside; there's going to be much more to this story that we'll have to wait and find out about.
"Extremis" also sees Nardole take a step-up to becoming more important to the Doctor and Bill, making sure he is absolutely needed and not just in the background, reminding the Doctor to look after the Vault. Bill's personal life is building piece by piece, as well as her relationship with the Doctor, as we see their relationship move onwards from the madman with a box stage to actual people who see each other (no pun intended) as real people, despite their flaws and can still rely on each other.
The Monks were terrifying and so well done. From the way they move, look, speak, it was all brilliantly done. It was a perfect build-up for the following episodes, as well as being an incredible episode on its own with many rewatchable qualities that can be enjoyed time and time again (which has been quite rare these past few years).
{On a side-note, many of the people who have disliked the episode seem slightly confused about the story and don't fully understand it, so they could probably do with a re-watch. Some also don't like the Vault reveal, but I already explained that it makes perfect sense and shouldn't be/couldn't be anything or anyone else. Many other negative points they make is never truly justified and makes it clear they dislike the episode for no real reason.}
Episode 6 "Extremis" - 10/10