I've got to admit that this remains one of my favorite tales, for several reasons. For one, I think it's one of his most successful forays in the realm of (more-or-less) traditional horror, dealing with something close to necromancy (the quote from Petrus Borel to the contrary notwithstanding). For another, his extremely careful blending of genuine and mythical history is astounding; especially given that there are several elements in this short novel that one would take to be pure fiction that are actual history, and vice versa. It also brings Providence to life as a character rather than a simple setting, which is something I always enjoy (seeing setting become a character in a tale). It is, in truth, near a love-song to his hometown. And his achievement with the tale set in the late 17th through the 18th centuries is damned near unsurpassed by any modern writer in the field (Hodgson, for all his strengths, was absolutely atrocious at this aspect). As with Hawthorne, Lovecraft here achieves an historical depth to his story that is quite impressive, to say the least, and his use of his growing mythos is kept to a minimum touch, to add an allusive quality that avoids explicitness. Some of the concepts he addresses here, too, are very impressive, the more one thinks about them, such as the outline that Dr. Willett sees in the pit; Lovecraft here gets the reader to actually trying to envision something so outside the geometry of our reality that it becomes an assault on reason and emotion by its mere existence, and I think he handles that quite well.
I know that Lovecraft felt it was a bit of "creaking antiquarianism" but I've always found it to be a superb performance, and I'd continue to count it as one of the better novels in the field from the twentieth century. It's a book that continues to grow more impressive on each reading, and the more carefully it's read, rather than less, and that's something not too many seem to manage.