One caveat here: I'm only about a third of the way through The Essential H.P. Lovecraft Collection (Golgotha Press) because, honestly, I'm not sure who among us could read 800+ pages of his material at a stretch.
That said, I don't think you need to read 800 pages in order to gauge your opinion of Lovecraft's work. After years of reading things by Richard Matheson, Stephen King and Clive Barker, I'd always heard about H.P. Lovecraft as an influence, but had never explored his material, myself. The Closest I'd come was seeing some of the film adaptations of his work, like Stu Gordon's Re-Animator. After finally doing so, I'd have to say he's something of a one-trick pony.
Lovecraft does a great job creating atmospheres of dread (At The Mountains of Madness, Dunwich Horror, the aforementioned Herbert West: Reanimator) and his Cthulu mythos of ancient entities/gods is interesting, but everything begins to follow the same formula: A survivor narrative of mankind encountering forces and creatures beyond their understanding recounted with exceptionally vague descriptions.
They say film adaptations (of horror stories, in particular) never live up to the source material because whatever the filmmakers envision can never live up to what the reader conjures up in his/her mind. Lovecraft feeds into that by limiting his own descriptions, instead relying on things along the lines of "unnameable," "beyond understanding," and "words cannot describe etc., etc." An interesting device, but when it's the first club out of the bag--and the second and the third--it gets a bit monotonous. Not saying I need everything spelled out, but if each tale exhausts the thesaurus of its synonyms for "indescribable," it starts to come off like a bit of a crutch.