Its genre is fantasy novel.
Rowling's writing is whimsical and rhythmic, with a lot of irony and good flow.
Her humor in the stories is dry and witty.
She likes to write in limited POV in third person. She describes enough, but she also leaves the rest to our imagination.
She ties her life to writing.
She mix in her stories all kind of feelings, such as love, emotion, intrigue, happiness, sadness...
Her writings are intended for people of all ages.