Think of him as a "lad", a bit more "street" than his ancestor. A bit more rough around the edges. Picture him, in fact, played by Vinnie Jones, of the movies Lock, Stock, and Two Smoking Barrels and Snatch.
Sort of what I had in mind for a second-generation Holmes, in which Watson would be an uncle/mentor to the young Holmes heir, who would then develop a partner/sidekick/chronicler of his own...perhaps rather differing from the original long-suffering Watson.
Going for a straight clone of the old one would be a tad boring, IMHO. He'd have to fit in his new time frame and context. You could keep most of the old eccentricities, though, like the pipe and such, and his laboratory. He'd be just as intelligent and driven, but more comfortable moving about in the modern underworlds.
Perhaps in the fashion of the original Holmes in his own younger days. *Uncle Watson warned me about the dangers in this venturesome but necessary phase....*
As for Watson, I am adamant that she NOT be some young knockout. Her role would be best served by a middle-aged, proper lady, one offering a marked contrast to the younger, tougher Holmes. I HATE it when lazy writers set up an obvious romance, and one should not be here. I'd picture her as resembling James Bond's Miss Moneypenny in looks and demeanor, if not in her crush on her friend.
Sorta recalls Steed and Mrs. Peel, Don't it. And to, she might be the criminalist technician, commanding her own *Baker Street Irregulars* in specialized forensic fields....
Developing....
Great minds DO think alike. I had Watson in my concept imagined as a physician herself...a forensic pathologist for Scotland Yard. I see her as a widow, about 50, but still quite attractive and of good breeding. She might have one child, with whom she speaks frequently, a daughter.
Let's say, she examines a murder victim whose corpse provides more questions than answers. Unable to come to any conclusions, and with the Yard baffled, she remembers the old stories her family told her about great-grandad's best friend, and that that legendary detective has a descendant who shares his interests, and who ALSO has a reputation with the police, although not one nearly so respectful.
I picture the new Holmes as having grown up roughly, on the streets of London. He might have military service in his record...perhaps as an Enlisted SAS operator. In his mid-thirties now, he has educated himself well, and makes a comfortable living in his work. He has the legendary deductive skills, talent for disguise, and scientific knowledge of his forebear, but also the street-smarts that came with his youth on the mean streets. Although he also has classical knowledge, he has yet to lose his Cockney accent, or his willingness to use fists as well as his brains, a facet of him which proves surprising and somewhat dangerous to the proper Ms. Watson.