And before this turns into another "Is Mary good or evil" thread,
I think there are a lot of fantastic villains in ACD's stories that could still be used in the show, whether with a modern twist or just as they are.
Baron Gruner is a bit of an old-fashioned villain, really, because the perception of relationships, starting them and ending them, and the consequences especially for women, have changed so much. But I can see how he'd still be an interesting antagonist, with his cold-hearted but totally mesmerising manner. Maybe his modern version could be not so much a Victorian womaniser but someone who ruins people in a different way, maybe a drug baron or a pimp or what have you.
I like "The Illustrious Client" especially because it has such a good ending - the villain is not killed or taken to prison, but he is still permanently neutralised, with a lot of time left to him to think about his crimes and repent. And I think that Doctor Watson really shines in it, too - he's doing everything in his power to help the cruelly injured man even though he's a ruthless murderer, while Holmes is only concerned with securing the evidence of his crimes. Sherlock Holmes solving the crime but John Watson saving the life, once again. 
Another brilliant villain that comes to mind is Bodymaster McGinty of "The Valley of Fear". I don't read that book very often because the part of it that is set in the US literally feels like a heavy weight on my chest whenever I do. But McGinty and his mafia are a brilliant creation that I could easily see transferred to the UK and used in a modern episode (and Sherlock more or less playing the part of Birdy Edwards).
There are a lot of secret societies and mafia-like organisations in ACD's stories and we've barely seen any of it yet in the show (other than the Tong in TBB; Moriarty's network doesn't really count because we never actually see any of it at work, except the man himself). I'm sure there's more of that to come.
Last edited by La Jolie (September 27, 2014 7:45 am)
BrettHolmes wrote:
, I feel that she's written as a villain so far. That could change in S4. I love the way Amanda Abbington has played her, and the switch from likeable to sinister. I also like the idea of changing the character of Mary. I liked Mary in the book, but she was a rather old-fashioned character, and I'm enjoying seeing a stronger, more interesting female character with a more central place in the story. 