Is it a comedy? What era would it be made?
The seventies.
It's a mostly serious work--but there's some differences.
Holmes would be more of a dandy and a bohemian (more Robert Downey Jr. than Benedict Cumberbatch, so to speak), and Watson (who is the son of Mary Seacole) is more down to earth.
There would be a more gritty, realistic portrayal of life in Victorian London. In one of the original stories,
The Green Poppy (set in Limehouse, then Singapore and Hong Kong), Watson comments "I wonder why they chose to live here". Holmes sarcastically replies "To get away from civilization, of course!"
Also, since I'd imagine that the martial arts movie craze of the seventies would still happen in this timeline, Holmes would get to use his cane skills a lot more, and Watson would get to show off his army training.
And, of course, Irene Adler would get a more prominent role. (Not as a love interest for Holmes, though--the writers felt that it would stray too far from Arthur Conan Doyle's vision of the character)
I did consider giving the Watson role to Harry Belafonte, but I realized that Pryor and Wilder already compliment each other as a comedy duo, so why wouldn't they work in a more dramatic role?