Disappointing. Gallifrey was completely underused- and trust Moffat to just handwave away how the Time Lords got out of the pocket universe, which is even worse since he said that we would be revisiting Capaldi's scene in DoTD in this episode!
New Sonic gets a thumbs-down from me. Looks like a lightsaber. Clara return gets a massive thumbs-down for me- it completely cut off the Doctor's emotional reaction to her death back in Face the Raven. Vanilla TARDIS gets a thumbs-up. As with the rest of this series, Ashildr's become better every time we see her, which I like- by now she's actually an interesting character, instead of the naive Viking she was in The Girl Who Died.
The Christmas special is looking really good- I feel like a comedic Christmas special is what we need after Last Christmas and The Time of the Doctor.
Overall, I give Series 9 a 7.5/10- it had some amazing episodes (The Witch's Familiar, The Zygon Inversion, Under The Lake and Heaven Sent, I'm looking at you) but Heck Bent and Sleep No More really pulled it down from the 9 that I would have given it otherwise. Definitely a massive improvement over Series 8, though- I'm looking forward to Series 10.