Definitely the weakest of the season for me so far, but not a bad episode.
I just saw the 500 year diary the other day in The Power of the Daleks, so that was a nice reference with the 2000 year diary. I was happy to see the sonic glasses get crushed right away, so I'm hoping they don't return.
The story was kinda average. It felt a bit rushed after The Doctor came up with the plan. I also don't like what they're doing with Clara this season. I'm sure this is all related to this being her final season and is leading to whatever they have planned for her sendoff, but given that there's a vocal subset of fans who seem to hate her, it's not a good direction.
I also felt that after the initial attention brought to his face in Deep Breathe, his revelation in this episode was a bit of a letdown. It was cool as a callback, but is that it? His face was just a reminder? Is that even something he needed to be reminded about when he regenerated?
The best part of the episode was turning Maisie Williams immortal, but from the trailer for next week, the payoff doesn't seem all that interesting.