I enjoyed that a lot. I admit, I was a bit nervous when I realised that the series finale was being written by Steve Thompson, as his episode last year wasn't as good as the other two, but I think he did this one proud.
I've not read the original - although I think that knowing what happens at the Reichenbach Falls is somehow sort of ingrained in most Brits, isn't it? - but I seem to recall that while Moriarty was trumpeted as the most amazing criminal mastermind the world had ever seen, there wasn't much evidence for it in the story. (I'm only going on other adaptations of it that I've seen, I'm afraid). So it was rather a nice touch here for that to be rectified; Moriarty clearly is amazingly clever, albeit totally bonkers. Not only does he construct an elaborate plot to discredit Sherlock, he checkmates him at every turn, having thought of everything (bar that one thing at the end) which could possibly work against him and has some sort of insurance against it. I rather liked the fact that the magical computer code was a macguffin all along, and that Moriarty's break-ins at the beginning were in fact organised using those good, old-fashioned methods of bribery and blackmail!
Steven Moffat and Mark Gatiss both tweeted within minutes of the ending that "of course there'll be a third series" and that it was comissioned at the same time as the second. I hadn't thought a third series was in doubt, but it's good to have it confirmed.
Martin Freeman was - as usual - terrific, and in that final scene at the graveside he was just heartbreaking. If I have one niggle, however, it's about that final shot of Sherlock watching him. One minute, we're watching a lovely tribute from a devastated friend which was very moving, and the next, it turns out it's for nothing. I admit, I was wondering if we'd get something like that, or if we'd be left assuming Sherlock was dead - I'm sure there are enough people out there who aren't familiar with the fact that, having killed off his creation, Conan-Doyle later resurrected him, so it would have been feasible to have left it at "he's dead". Conan-Doyle did, after all! Or was there a fear that if the audience was left believeing their hero had died, they wouldn't tune in for a third series? (I assume S3 wouldn't have been called "Watson"!)
Personally, I'd have preferred it without that shot, but then I already knew Sherlock wasn't going to die.
Anyway, a good job by all concerned on this one. I expect there will be an inordinate amount of theorising about the "how" in the next few months. Molly obviously had something to do with it (she probably supplied a suitable corpse!), and presumably, the cyclist knocked John down on purpose so that he wouldn't be able to identify the body. Sometimes the simplest explanations turn out to be the right ones :-)