5. It's Sheer Continuity Porn
I'm not one to frequently throw around the term "Continuity Porn", but for a seven minute minisode there's just no other way to describe The Night Of The Doctor. The Eighth Doctor returns for the first time since 1996 (along with his Sonic Screwdriver) and mentions his companions from the Big Finish Audios (more on that later), and the Sisterhood of Karn make a comeback in a huge way. When did we last see them? The Brain Of Morbius in 1976. How many TV appearances did they have before this? One. Steven Moffat takes this single element from The Brain Of Morbius that has largely fallen into obscurity and makes it a crucial part of a much larger story. The same goes for their Sacred Flame and, more importantly, their Elixir Of Life. It was a one-off part of a thirty-seven year-old story and is now a cornerstone of one of the most significant events in the programme's history by inducing and manipulating the Eighth Doctor's Regeneration. And just as a final little nod to the past, the Karn priestess in The Night Of The Doctor is named Ohila. She's never directly referenced by name and was given that name purely to imply a connection to Ohica (a member of the Sisterhood in The Brain Of Morbius) and make the ties to the past even stronger.