This show is unbelievably awesome! I love everything: music, cast, characters approach and the modern adaptation of Doyle's stories. I'm not so crazy about the Moriarty portrait because I would like to think that the perfect villain is above the psycho category.
Everything else is as good as it gets, for sure. And I'm guessing the short amount of episodes per season is to focus all efforts in creating it more interesting. Every episode ends with a moment which will make you think, How did that happened?