The finale landed pretty flat for me. There were a number of specific issues I had (top of the list being where the Doctor deliberately commits genocide on the Sontarans without so much as a "Have I the right?"), but more generally it just felt insanely rushed and nothing got the time it needed. It seemed like the writers spent the entire episode sprinting from one plot thread to another, trying to tie them all off any way they could.
Looking back over the serial, I think it would have been vastly improved by scrapping Swarm and Azure and all the weird "time versus space" stuff, along with the Great Serpent and the separated lovers searching for each other, and the totally random addition of the Mad Mole. It isn't that any of those elements were bad; in fact most of them could have been quite good if given stand-alone episodes in which to breathe. But this story really wanted to be about Division unleashing destruction on the universe, and the Sontarans trying to take advantage of it.