Lovecraft notoriously relies on mood rather than piddling concerns like dialogue or plot, so it's perhaps not surprising that his longer works falter. That's particularly true in this collection, which contains the mind-numbingly dull "The Dream-Quest of Unknown Kadath," which left me longing for a Lovecraft/Nightmare on Elm Street crossover wherein I could send Freddy Krueger after Randolph Carter to finish the meandering bastard off once and for all.
The other issue with this particular collection is that most of the tales, like the aforementioned horror that is "The Dream-Quest", are set in worlds totally of Lovecraft's fevered imagining, which seem to sport a lot of showy lapidary work but not much else. Characters move through strange realms as if there were a spotlight upon them, illuminating only what they approach without ever giving any kind of clear view of the world as a whole (or why all the realms seem so hung up on decorative stone work). Frankly, the author's work is more effective when he brings this kind of nebulous feeling to a more familiar setting, like his storied New England. That breeds horror; the other just breeds the desire for a roadmap, a good flashlight, and possibly a fence who deals in lapis.
Still, if for no other reason this collection is worthwhile for the inclusion of the three page short "The Book," which is utterly delightful for taking the concept of books changing your life and turning it on its head and giving it tentacles. Sadly, this book fails to pack the punch of that story's worm-riddled tome.