Granted, it's been almost 20 years since my Sherlock Holmes phase, but I think Anthony Horowitz did a creditable job. He respected the original timeline, characters, narrative structure and voice. The plot was interesting, and even though it would have been a bit risque for Conan Doyle's time, it was handled delicately enough. My only criticism is that Holmes was a little too human. I'm used to a Holmes that's less than likable.
This book made me cry and laugh...sometimes at the same time. Parts frustrated me (characters' endless internal speculation, for example), but other parts gave me chills, so I'm definitely in for round 2 in All Clear.
Enjoyed it a lot, except for that Jennifer woman. I hate her so much, it made me lose respect for Lucas. I guess that's the sign of a good writer: provoking strong emotional response.