(Further space for spoilers for those reading this on non-LJ platforms)
Stuff I particularly liked:
The best scene, as many others have said, was the cafeteria conversation between Wilf and the Doctor. Bernard Cribbins is generally excellent. What an extraordinary break it turned out to be for Doctor Who, when Howard Attfield was too ill to continue as Donna's father, and Cribbins was brought back in!
I also thought John Simm much better here than in Season Three, where (heretically) I wasn't actually all that impressed by him. There seemed to be more to the Master this time, perhaps because he isn't in control for most of the episode. The Master transformation (as someone put it, the Tremasization) of humanity was a great concept, and the Obama thing worked for me, though I note not for everyone.
And I unashamedly loved the end. We knew it was coming - we have known it was coming since the first set photos of Timothy Dalton leaked out - but I love the idea of the Time Lords returning. I particularly like the possibility that their return may actually be a Bad Thing which the Doctor will give his life to prevent. I don't think there is any chance that Claire Bloom's mysterious lady character is actually Romana; sorry, folks, I don't think that is how RTD's mind works. The Deadly Assassin is seen by many (including me) as the zenith of Old Who, as Robert Holmes, its greatest writer, tackled the Doctor's own origins. RTD has set himself a similar challenge here.
I was a bit more ambivalent about the plot, or lack thereof; my expectations of RTD on this score are fairly low and I suppose they were met. I hope the Vinvocci aliens get a decent shake of the action and don't come in for just that one scene. I hope the Nathaniel and Abigail plotline also has a halfway decent resolution. I hope poor old Wilf and Donna aren't killed off. I hope Wilf himself doesn't turn out to be a Time Lord in disguise, or (as some think) to be concealing the whole of Gallifrey in his mind.
The one bit, well, two linked bits, that I thought over the top were the secret cult of the Master bringing him back - OK, it had to happen somehow I suppose, but it seemed a bit silly; I think I would almost have preferred his unexplained escape from the certain doom he faced at the end of his previous story which was the Old Who approach - and the resurrected Master having the powers of shooting energy from his hands, which he mysteriously doesn't actually use to kill the Doctor and which equally mysteriously desert him once Nathaniel and Abigail have got him. But Simm in general made up for it and was creepy and yet comprehensible.
The companionless Doctor: Picking up on the cafeteria conversation, I've just been watching both The Deadly Assassin and The Massacre, the former being the only companion-less Old Who series and the latter ending with a scene where the First Doctor's companions have all left him. The Doctor does need someone, and it's been part of Ten's tragedy that it hasn't worked out. (Incidentally, both stories feature actor Erik Chitty - in The Massacre he plays Charles Preslin, the scientist who conceals the Doctor from the main narrative for three episodes, and in The Deadly Assassin he is Coordinator Engin, in charge of the Matrix, who shunts the Doctor into the alternate world of the Matrix for two episodes.) Ten has now had three TV specials without a regular companion, as well as a large number of books (including the ten-volume Darksmith Legacy series). His slightly silly opening scene (including the dogy line about Good Queen Bess) gives cover for all of those being canon, for those who care about such matters. (And was there also a reference to Netty from Beautiful Chaos?)
Next week, I reckon that we will get the mother of all reset buttons, and not only will the Time War be reversed, but so will all of the Doctor's incarnations taking us back to Matt Smith as a younger version of William Hartnell. That will of course create problems with River Song's return, but Moffat is the master of timey-wimey stuff so he will have thought of an answer.