From The New York Times:
Holmes, described by Conan Doyle as “the most perfect reasoning and observing machine that the world has seen,” isn’t actually a particularly likable character, or even a very fully realized one. Raymond Chandler once remarked that Holmes “is mostly an attitude and a few dozen lines of unforgettable dialogue.” He is languid, aloof, arrogant, supercilious and a bipolar druggie who in “The Sign of Four” is shooting up cocaine three times a day to overcome his lassitude. He has no friends other than Watson, and Mr. Lanza notwithstanding, he is almost certainly a virgin. In fact, there is something slightly inhuman about Holmes, though somehow that only adds to his appeal. We’re fascinated by him, it seems, precisely because he is a kind of cipher, unlike anyone else we know or even have read about.
The recent additions to the sagging shelves of Holmesiana suggest some other clues to the mystery of Sherlock’s appeal.
More here.