To my surprise, it's a gimmick that works. It dispenses with all the baggage of recreating Victorian-era London and faithfully recreating the plots of Sir Arthur Conan Doyle's canon, instead hewing closely to the spirit of Doyle's stories. I normally prefer fidelity to the original material in adaptations, but since we've already had a very faithful Sherlock Holmes series via Jeremy Brett, I'm fine with exploring alternatives.
The pilot episode, "A Study in Pink," contains various references to the canon, some as easter eggs planted for fans, others which are similar yet different to the canon (such as the pilot's title, cribbed from A Study in Scarlet, 'natch). As in the canon, Dr. Watson is a wounded war veteran, he and Holmes become roommates at 221B Baker Street, and Lestrade brings Holmes in on cases as an unofficial expert. Much is made of Holmes' staggeringly anti-social personality, as he can't abide dealing with people less intelligent than him, preferring to solve crimes in order to achieve satisfaction. Instead of a tobacco habit, this Holmes uses the more socially-acceptable vice of nicotine patches; mind you, he uses a few too many of those.
Based on the pilot, it's very faithful to the original concept of Sherlock Holmes, although actor Benedict Cumberbatch is about the most arrogant Holmes I've ever seen. Taking it's cue from modern mystery programs like CSI, Sherlock makes strong use of know-it-all experts making huge leaps in logic based on flimsy evidence, but I accepted it here; it's Sherlock Holmes.