See also Last of the Time Lords, Mass Effect 3.
The thing about Last of the Time Lords that's interesting, I think, is the whole Doctor on the run thing. The Master being the PM gave at least the first part of that this real weight. There's some really great scenes. I love the Master gassing his cabinet, the tense phone call between the Doctor and the Master, and the moment Martha's family is arrested and they're forced to go on the run. It's everything the Doctor is best - anonymous, mysterious - turned on its head. Suddenly he's wanted, and it works really well for that particular story.
The next week starting a full year on in this sadistic, fascist world is great too - there's just two key problems - first, the conclusion, and second the implementation of the TARDIS being turned into a Paradox machine - it's just sort of there, and the reveal carries no weight. Oh, and the barely-characterised but super-clear transformation of his wife from a twisted mirror of Rose to an abuse victim is great. I think there's some great ideas expressed in that story overall - but the two things that resolve it - the Paradox Machine and Jesus Doctor - are really, really bad.
The finale probably jumps around lots of different time periods like The Big Bang and The Wedding of River Song. I suppose the crimson horror is placed so late in the season just to remind viewers about Vastra, Jenny and Strax?
A more realistic reason is probably them just wanting to put a gap between the two Gaitiss episodes so his 'style' doesn't dominate too much.