That was one of my first books, actually. I got anything as a kid that was about monsters or ghosts and found this in a bookstore when I was like 7 or so. The stories(obviously) took some time to know, but they were spooky and wonderful. "Oh whistle and i'll come to you, my lad" is one of the best ghost stories. And "Casting the Runes" is an all-time classic, among others.
Recently, i've been reading Algernon Blackwood and Albert Machen, also expert practicioners in the macabre. Machen and Blackwood created the genesis of what Lovecraft would follow up in his cosmic universe. Tonight I read H.G. Well's "The Red Room", a very creepy, if underrated, spooky tale that really gave me the chills!