The magic in the movie is NOT systematic. I thought that the resolution of the main conflict of the movie rested entirely too much on "things just working that way". I did not read the books. The rest of my family, having read the books, thought that the movie was a faithful adaptation. Their minds could fill in the logical gaps in the movie, whereas I could not.
Fellowship of the Ring was way better. Harry Potter = quaint British childnren's story reasonably well done. LOTR = epic, LARGER than larger than life, fantasty film.