After the wonderful episode that was 'Heaven Sent', 'Hell Bent' feels like something of a let down. If you take the last three episodes of the season as one story, the second part was definitely the strongest. That doesn't mean, however, that there weren't a few moments of greatness in the series finale.
The Doctor's back on Gallifrey. After believing it lost in the Time War, then saving it but not knowing where it is The Doctor is finally home. And what does he do once he's home? Well, he takes over the planet without having to even do anything.
In a sequence that's a moment of pure genius The Doctor returns to the barn seen in 'The Day of The Doctor' and 'Listen', that has a connection to where he grew up, and immediately attracts a crowd of Time Lords who seem to hang on his every action. Rassilon, last seen in 'The End of Time' played by Timothy Dalton, now regenerated to Donald Sumpter, sends out a gunship to bring The Doctor to the capital.
The Doctor simply ignores the ship, so Rassilon sends The General and a squad of soldiers, who he ignores. Next it's the High Council, who he again ignores. Finally Rassilon himself must face The Doctor, and it's clear that the two Time Lords hate each other. Rassilon orders the soldiers with him to gun The Doctor down, yet none of them do it, instead switching sides and joining The Doctor.
The Doctor has effectively deposed Rassilon and taken over as the ruler of Gallifrey, and he didn't even have to lift a finger to do it. It's because not only is Rassilon a major douchebag with questionable morals, but because even on Gallifrey The Doctor has become something from legend. The soldiers sent to face him are in awe of him, they know what he's done in his life, and in the Time War, and they know he's without a doubt the wrong person to ever cross.
Watching The Doctor become the ruler of his people, again, without having to do anything is brilliant. It shows just how amazing the character is. Everything he's done, everything that makes him who he is makes him a figure to be feared, respected and almost even worshipped even by the most powerful race in the universe.
From here the episode takes an interesting and unexpected turn, as the whole issue of the Hybrid is thrown aside as it's revealed that the only thing The Doctor actually intended to do by becoming the Lord President of Gallifrey was using Time Lord technology to try and save Clara, something he knew they'd never allow him to do.
The Doctor finally has his home back, he's respected and revered by his people and he can do whatever he wants, and he's willing to throw all of that away just to save his friend.
The scene in which The Doctor saves Clara from the moment just before her death is one that is sure to be well remembered for two reasons. The first is that The Doctor shot and killed someone. Yes, that person is a Time Lord and has the ability to regenerate, but regeneration is something a Time Lord has to consciously do, there was no guarantee that The General was going to be able to regenerate in time before he died. Also, when a Time Lord regenerates they do in a way die and become a new person, The Doctor has even said that himself. This is a scene that does away with the modern 'no guns, no killing' Doctor and starts to bring back an aspect of the classic series, that if the stakes are high enough The Doctor will commit murder.
The second thing that this scene will be remembered for is the reinforcement of the rules of regeneration. We've known that Time Lords can change gender when they regenerate, the concept was brought up in 'The Doctor's Wife' and made very clear when The Master became Missy. We know that Time Lords can change ethnicity, we saw that in 'Let's Kill Hitler' when Mels regenerated into River Song. But this episode erases any doubt or argument when The General regenerates from a middle aged white man into a young black woman. As when Missy was first introduced, this is surely a way of guaging public reaction to Time Lords changing in such a way, possibly in anticipation of something similar one day happening to The Doctor.
From here the episode became all about The Doctor trying to save Clara, and actually failing to do so. Despite how the episode ends, with The Doctor having mostly forgotten Clara, Clara still technically not being alive as she's frozen in time, with Clara and Ashildr/Me flying off into space and time in their own Tardis Clara is still eventually going to have to return to the trap street and face the raven.
It's made very clear that Clara isn't off the hook, she will eventually have to go back to Gallifrey and be sent back to the moment of her death, but she;s been given an extremely long stay of execution, essentially able to spend an eternity with another undying woman having adventures in space and time. After how the death of Clara was handled in 'Face The Raven', and the fall out of that event in 'Heaven Sent' this feels like a cheap way out. Moffat has killed the character, but still gets to give her an ending that will keep Clara fans happy. It just feels like a bit of a cheat to those that liked the way she died.
One thing that absolutely has to be spoken about though is the inclusion of the original Tardis interior. In a moment of pure fan service, that makes a hell of a lot of sense in the context of the show's universe, The Doctor steals another Tardis, one that has the same control room as the original William Hartnell Tardis.
Yes, this is quite obviously a little treat for fans of the show, it's nostalgia and fan service, but it also adds something to the show. It's saying that the original Tardis interior wasn't something that The Doctor chose, like he has done in later incarnations, but is the standard default control room that all Tardis' have.
The episode ends with Clara and Ashildr/Me off to have adventures in their own American Diner shaped Tardis (why that of all things?) and The Doctor ready to continue on, to find a new companion and keep on being The Doctor. He dons his velvet jacket, grabs his new Sonic Screwdriver (which is a thing of beauty), snaps his fingers to close the Tardis door and head off to even more edventures.