The question is not whether 'The House of Silk' is good (because I believe it most certainly is) but whether it is superior to Conan Doyle's full length novels about Sherlock Holmes.
If the suggestion that a new Sherlock Holmes novel could better than the original sounds to you like sacrilege; and if, sensing the blood boiling in your veins, you feel compelled to write a blistering epistle; then I would ask you to wait a moment. For please note, I have limited my comparison to the full length novels of Sherlock Holmes and not to the short stories. It is my belief that the short stories might never be surpassed but I will argue that, with the publication of 'The House of Silk', the longer tales have been.
Consider my case: it would take a brave Holmes enthusiast who would argue that three of the four original Holmes novels reach anywhere near the pinnacle of Conan Doyle's achievements. 'The Sign of Four' or 'The Valley of Fear' seem tedious when compared to some of the great short stories like the adventures of 'The Speckled Band' or the 'Red-Headed League'. Even 'The Study in Scarlet' fails to reach the heights achieved in the shorter stories. But 'The Hound of the Baskervilles' is a different matter. This gripping tale has rightly achieved international fame not only as a novel but in its many manifestations in the cinema. For millions of people the names of Baskerville and Holmes are almost synonyms. If I am to argue that Anthony Horowitz's novel is superior to any of Conan Doyle's originals then it is 'The Hound of the Baskervilles' which sets the bar that I must vault.
At this point I must introduce a second refinement to my argument. My first was that I was talking only about the novels and not about the short stories. My second qualification is that any true Holmes novel must be built firmly on the foundation of Holmes' personality. For surely if a novel is to be a Sherlock Holmes story then its essence must be based on his persona: his cogitative powers; his misogyny; his latent, but all too excusable, misanthropy; his penchant for disguise; his drug abuse and perhaps that disdain for the conventions of the law displayed in many of the short stories, for example in the final paragraphs of 'The Adventure of the Blue Carbuncle'. If we can substitute some other persona into the story, causing only the minimum alteration to the plot, then it could be just as well be, say, a Hercule Poirot story or even (admittedly grossly displaced in time and space) a Philip Marlowe tale.
Now, although I believe 'The Hound of the Baskervilles' to be marginally the more gripping novel, 'The House of Silk' is, I contend, superior as a Sherlock Holmes story because it is founded wholly on the character of detective himself. To understand my point please consider the extent to which Sherlock Holmes' personality defines the course of events in 'The Hound of the Baskervilles'. Ask yourself to what extent his deductive reasoning is critical for its development; whether the essence of the protagonist is more that of a bodyguard than an investigator; and whether the attraction of the novel lies in gleaning evidence from the crime scene or from its (almost melodramatic) terror. (By the way, Conan Doyle was good at 'terror' or 'horror' as we might now call it - terror having acquired a political nuance. His 'Tales of Terror and Mystery', which is available free on the internet, makes enjoyable reading.)
I am not sure that there is a clear answer to these questions but it is surely apparent that Conan Doyle in writing 'The Hound of the Baskervilles' was prepared to forget Holmes' talents if he felt that an escalation of terror was demanded. How else can we explain, as Sir Henry walks alone across the moor, Holmes' confession that the great detective had not reckoned with fog on Dartmoor? The approaching fog is good for heightening the evolving horror but it is fatal for Sherlock Holmes' cogitative reputation. Not reckoned with fog on Dartmoor! It's like admitting not having anticipated sunshine in the Sahara.
Now beware, 'The House of Silk' proceeds at breakneck speed. The game is continually afoot. Once started there is no time left for the unimportant tasks of life, like shaving, reading emails or putting the cat out; each page will grip you as firmly as a vice. But nowhere is the persona of Holmes sacrificed for the adrenalin rush. His character might not be substantially developed (although that of Dr. Watson certainly is) but it is not diminished. The scenes are vividly described; you can feel the winter cold, taste the yellow fog, smell the fetid river Thames and hear the cacophony of late nineteenth century London. Yes at the heart of 'The House of Silk' lies a sordid darkness, but there are few Holmes stories that do not deal with the endemic evil in the lives of the rich or the powerful in Victorian England. Anyway any bleakness in the book is obliterated by gloriously atmospheric scenes: the dismally lit passages in the docklands, the flamboyance of Dr Silkin's circus, Holloway's barren prison and, of course, the wretched decadence of the house of silk itself.
I am left with two wishes:
the first is that in some obscure Hollywood office the idea of making a movie of the book will be born (but there is a nightmare scenario: not realising that 'The House of Silk' is no romp-around, the office phones Robert Downey Jr.'s agent).
My second wish is for a sequel. Anthony Horowitz maintains that 'The House of Silk' will be his only Holmes novel. Like Conan Doyle he wishes to be freed from the shackle of future tales. But, I suspect that, like Conan Doyle he may have been too successful to escape this fate. Excellence is a virtue and as Nietzsche noted: we are punished most for our virtues.