This book is excellent, and not just for people that love a metric ton of references to other works, and "alternate history" stories. I truly believe that it stands well enough just in the category of a follow-up to Bram Stoker's Dracula, and if you just really loved Dracula, you should like this book a lot.
First of all, it's extremely well-written, so even the parts of the book that drag a bit are satisfying to read. If you DO happen to be a massive literary, history, or vampire fiction fan, you'll smirk and chuckle at innumerable references to other works, but honestly, the way Kim Newman handles the Prince of Darkness himself is worth the price of admission.
Dracula is hardly in the book at all, and that is the PERFECT way to handle him. The original literary Dracula is nowhere near the misguided, tragic figure of Coppolla's 1992 film adaptation. He is plainly a monster, a creeping plague and a fiend, and Kim Newman takes the unusual approach of retaining that character profile, rather than making Dracula more sympathetic. However, like in the Count's titular novel, he looms over the entire story, and his influence is felt constantly. Characters talk about him throughout the story, and you're never really sure who is characterizing him fairly, which has the exciting effect of leaving you waiting in suspense for his inevitable reveal. More than that I won't spoil, but if you're a fan of the original Dracula, you'll see the character return here, perhaps for the first time. That said, this book is traditional third-person prose, not epistolary like Stoker's novel. It takes a bit of adjusting to.