Sussex Vampire has all the essential elements of the best Sherlock Holmes stories: a dark atmosphere, a believable mythical setup, a credible rational explanation, impeccably paced plot, and very real, raw characters, including Watson's old rugby rival, a typical burly and simple-minded Englishman. True, it does not feature as much of Holmes' typical flair for deduction, but the quality of everything else is still top notch.
One of the fascinating achievements of the series is Dr. Doyle's own observation of human relationships and psychology. He did this without the Victorian moral framework, which perhaps thanks to his profession and lack of religiosity. Like Holmes, he took a no-bullshit but still compassionate view of the poor bastards who get themselves in all kinds of trouble. He was unsentimental but fundamentally humanistic.
The startling revelation in the Sussex Vampire is how boldly and matter-of-factly he reversed the conventional wisdom that children are honest and pure. It is so true yet so rarely acknowledged. This story is so psychologically astute that Rene Balcer adapted it into one of the early Law and Order episodes.
In the story, Holmes' sensitivity to and empathy for others' emotional states are again on full display. A surgeon may have an absolutely steady hand when he cuts the patient open, but it doesn't mean he has no compassion for the patient. This attitude, which may seem a bit cool to some, is common and natural in medicine. Holmes may not be the most touchy-feely, sentimental chap in England, but his possession of a heart is clear as day when he told the client/the husband:
"Mr. Ferguson, I am a busy man with many calls, and my methods have to be short and direct. The swiftest surgery is the least painful..., but in doing so I must wound you deeply in another direction."