Still an effective horror story, whose biggest strength lies in its detailed setting. Lovecraft was a fan of the story, and it strongly influenced the latter's "Shadow over Innsmouth." Particularly recommended for Mythos fans, however the racial language may be very off-putting to some readers.
Accurately described as a classic in the field; it's frequently cited by most works on lycanthropy. Responsible for popularizing the mythical version of the Elizabeth Bathory story that continues to influence vampire fiction to this day.
Author's writing is entertaining enough that the book rates equivalent to above average fiction for the period. It's a quick read, but covers the material well.
The story should have been listed as mystery/pulp, since it's largely a crime caper. Still it does a decent job of building up the first half, but the back doesn't deliver. While far from the worst I've read, it's on the low side of mediocre. I say this as someone who deeply loves horror and pulp style fiction, and is at least an FWB to mysteries.