So. Much. Fun. My recommendation? See the movie first, then read this book, then see the movie again. Why? See the movie to experience it without any preconceived ideas about the plot, then read the screenplay to pick up on details that might have gone by too quickly to catch... and the watch the movie again, this time looking at the small moments, clues, interactions, etc that relate to the big picture, and possibly give hints of what's to come in future installments. 
 Spoken like a Harry Potter fanatic who believes, down to her tippy toes, that one time reading (or viewing) is never enough.