Overall, an enjoyable episode. A few quick thoughts:
Not much impressed. Soon fed up of Missy and John Simm's Master seems to be moustache-twirlingly over the top.
Bill is a Cyberman ..? Meh. Not invested enough in her and with the level of humorous quips and send-ups I am just not feeling any tension.
I fear a female regeneration but don't believe it will inject much-needed originality.
"World Enough and Time" has also been quoted as a title to one of "The Diary of River Song" audio stories from Big Finish. Also, two Masters apeared together earlier on audio as well. I liked the bit about time passing slower closer to the event horizon of a black hole. It's a bit hard to wrap one's head around the concept when there is a physical object, a ship, traversing the boundry.
It's a quote from Andrew Marvell's "To His Coy Mistress".