CAS probably has the richest, most lush prose of any other author of modern fantasy. Sometimes, you feel that his stories are lacking in plot and well rounded characters but that can generally be forgiven if you are willing to slow down your pace of reading and really savour the quality of the prose, much like fine wine.
To give you a flavour, here is the opening paragraph to "The Demon of the Flower":
Not as the plants and flowers of Earth, growing peacefully beneath a simple sun, were the blossoms of the planet Lophai. Coiling and uncoiling in double dawns; tossing tumultuously under vast suns of jade green and balas-ruby orange; swaying and weltering in rich twilights, in aurora-curtained nights, they resembled fields of rooted serpents that dance eternally to an other-worldly music.
That's not to say that all the stories are lacking in plot and interesting characters. But it is only fair to warn the potential reader that some of the stories contained in this collection are definitely pure prose.
Thematically, these are a broad range of tales of the fantastic, often quite dark, some bordering on horror. Some are even in the realms of SF but CAS seems to lack any concern for scientific plausibility.