This book won a World Fantasy Award. It's remarkable: the stories are rich, fascinating stuff — creepy and unsettling and phantasmic. Imagine what Tolkien's Lord of the Rings would have been like if Tolkien had tried to tell that story sympathetically from the point of view of the human denizens of Mordor and you'll have the slightest sense of what you're about to wade into ... but only just a sense.
These stories will make the same demands on you that they made on Brian: they will command and compel you, and fill you full of terrible wonder. And when you've finished them, you'll find yourself wanting more.