You're in for a treat with the Witcher books. My favorites are the first two short stories collections (I think their English names are The Last Wish and The Sword of Destiny, correct me if I'm wrong), which are prequels to the main novels. Because there, I dunno, there's an atmosphere that the main novels, although excellent, lack, I think because they become grander when it comes to the scale of the events. The short stories feel more... metaphysical... mysterious... I can't find the right word.
What's your favorite story so far?