As Vampire-book Sword & Blood is entertaining. You might take that with a grain of salt as it comes from somebody whose knowledge of vampire-literature is limited to Dracula (and that only because the audio-book-narrator was Richard E. Grant). I enjoyed the portrayal of vampires in this book. They are proper monsters, and the world which they rule is a grim and dystopian place. Also Athos' suffering after being turned into a vampire gets described in painful detail. For him there is no getting used to it or accepting his fate, he suffers all through the book. Despite this the rest of the book is cheesy and silly at times. (Sex-magic. There is sex-magic. And soul-saving masturbation).
As Musketeer-pastiche it's sadly only mediocre. D'Artagnan's name is misspelled throughout the whole book but at least his characterization is well-done. He is a rash teenager, both in Dumas' novel and in this book. Aramis' characterization is also well-done, even including some of his uglier character-traits. Athos is somewhat different from the original book but he is also (even more) traumatized than the original one and most differences can be attributed to that.
The only qualms I have characterization-wise are with Porthos for he doesn't get any. He gets described as shy, says about 10 sentences in the whole book and that's it. I also missed the feeling of genuine friendship that was so prominent in the original.
Those were men who without hesitation would risk their lives for each other without even demanding an explanation. There are dangerous situations here as well but the musketeers are united by the desire to fight vampires rather than friendship.
The book also contains my favourite pet-peeve: ending almost every chapter on a cliff-hanger. But at least it is combined with alternating POVs so it works more or less. (I still found the number of times d'Artagnan gets abducted ridiculous but at least it's done in a way that makes it exiting.)