I watched episode 1 of the first series last night (my first ever episode of Sherlock), so bear in mind that everything I say is based on one episode - and things may have been toned down in later episodes...
I thought it was brilliant, with the characters really brought to life for modern times. First impressions are that it's like a detective version of House (although it's clear that house was supposed to be like a medical version of the original Sherlock Holmes), but there are a few parallels with the anti-social personality and drug use (i'm guessing from the first episode that it's a recurring theme?).
Also the 'deduction' bit became a bit tedious, spelling things out to the audience where they could have worked it out themselves - but apart from that I thought it was amazing, and can't wait to watch the remaining 5 episodes!
plus, Cumberbatch is quite the fitty.