The rigorous scientism of the horror presages "Mountains of Madness" just as the rigorous historicality of the setting presages "Charles Dexter Ward." ("Cthulhu" takes from both strands, but lightly.) With "The Shunned House," Lovecraft has assembled almost his entire mature repertoire of themes, effects, and methods -- only the transcendence is missing, and this story is all the more impressive for its absence.
This despite the fact that its most notable overture toward cosmicism, the "titan elbow" of the thing in the basement, is just plain silly. Fortunately, the tremendous amount of scientific hugger-mugger Lovecraft deploys -- mentions of relativity, quantum mechanics, lines of force, and so on -- goes quite a way to cushion the blow. Indeed, the introduction of this scientific lore alongside with the (very authentic) ghost and werewolf lore collected in the earlier part of the story serves to emphasize the span of time between the primitive Huguenot vampire in the cellar and the present-day ghost-breaking Whipples, and to point up the multi-dimensional nature of the evil in the house.
I would go so far, contra Joshi (and contra Farnsworth Wright, who rejected "The Shunned House" when Lovecraft submitted it to Weird Tales) as to say that the slow, labored buildup of historical and spectral details and the equally dense justification that the modern, scientific Whipple narrator gives for the continuing horrors are both structurally necessary for the narrative (especially the pacing) to work correctly and thematically necessary for the transmission of the exact weird sensation -- of paranormality, not supernaturalism -- that Lovecraft intends. It's not quite as able and seemingly effortless as some of Lovecraft's later work would usually be (although anyone who finds this story "dry and long-winded" with a "bathetic" ending, as Joshi claims to, shouldn't be as fond of "Shadow Out of Time" as Joshi claims he is), but it's much, much better than the critical consensus seems to have it.
As a little lagniappe, I'll note that "The Shunned House" conveys the horror of the "common soul" we've noted before, as the Roulet vampire imposes (or impinges) its "lines of force" on others in the house and finally absorbs Uncle Elihu into its "multitude" of faces. One could draw some interesting lines from this story toward Lovecraft's hatred of "mongrelization," his fear of the mass man (he wrote this story while still in New York), his strong distaste for social pressures from economics to editing to marriage, his concern with degeneration (expressed here, as in "Cool Air" and perhaps "Doorstep", as deliquescence), and even his architectural mysticism (like "Rats," the monster is in some real way congruent -- sharing grue? -- with the house, although the implication of parasitism is stronger than that of symbiosis), or his pride in materialist mechanism (implying an absence of individual souls) and in his Augustan-colonial tradition (a "line of force" shaping his outlook just as the dead hand of Roulet does the Harris family). You can just keep circling around and around, looking at Roulet as the past -- still unnaturally present as with the Gothic, a survival of individual will that exists by breaking, deforming, and absorbing the will of others (Tradition), revealed through history and excavation (another metaphor for science -- or for self-knowledge, if you like), and so on.
And dude, Whipple Jnr. armors up with flame-throwers, a "large and specially fitted Crookes tube," sulfuric acid, and a gas mask, and he burns out the evil despite fainting! He weeps at his uncle's death, but the ghost is well and truly broken, and we end with the happiest ending in all of Lovecraft: "The barren old trees in the yard have begun to bear small, sweet apples, and last year the birds nested in their gnarled boughs." Providence is cleansed; Eden prevails. What a great story.
NEXT: "The Horror at Red Hook"