Arguably the original mysteries, these seem to have a stronger than usual appeal to the SF fan. As an anglophile I find them particularly attractive, and they're also interesting as period pieces -- perhaps more interesting than as mysteries.
Sherlock Holmes taught me a lot about how much society has changed over time. Many of the clues he used to determine the profession of a stranger simply don't work any more. Things are less structured and less stable and much more varied, and generally this is all to the good. It also showed me many of the better sides of the fairly rigid society of the time (the bad sides are pretty well known); for example, you could be a success within your class and station, rather than be considered a failure for holding a menial job.
Complete Sherlock Holmes