In my preparations for writing about murder, mayhem and an annoyingly intelligent detective, I was reading a good deal of Arthur Conan Doyle over the weekend- and of course as you look down and see my review, I ended my weekend watching the second episode of Sherlock.
I read "The Final Problem" and I can see why audiences were in a bit of an uproar, Doyle did not give a very satisfying conclusion to Holmes' story. It was ambiguous and somewhat anti-climactic. Moriarty was such a great creation as well (look at all the Sherlockian media he's inspired), kind of wasted on one brief story- though apparently in a post "The Empty House" story he is expanded on a bit.
However, his appearance does lead to this fabulous exchange in "The Final Problem":
"All that I have to say has already crossed your mind," said he [Moriarty].
"Then possibly my answer has already crossed yours," I [Holmes] replied.
This passage may be part of the wild speculation surrounding the third episode of Sherlock airing in the US next week on PBS. It certainly supports some theories, but could also be a ~red herring~ to throw our opinions in another direction, but I wouldn't be surprised if this passage is cited as evidence for certain theories regarding what's coming next season.
According to Moffat the key words for Sherlock season two are Adler, Hound and Reichenbach.