I rather liked Possession. I'm not sure i've read any LeGuin save "The Ones Who Walk Away from Omelas."

I suppose "fun action adventure story" is a decent summation of Rowling's world. Completely not a selling point for me, which is perhaps one reason why i'm not a huge fan. I really think you're right that she creates a world with great potential (hence my love for fanfic) but her storytelling ability is lacking (hence my dissatisfaction with the books).