I have done both (books and movie), and actually it is quite faithful except for a few minor grudges I had (since I am an ASOUE bookie). One was that the time spans they stayed at their relatives was greatly elapsed (I guess for running time reasons) and some of the plot events were out of order. But overall I loved the movie, and was very happy about how it was adapted. I'm sort of on the fence about Carrey as Olaf, as he overacts a lot. However, Olaf in the books does too, but his humor isn't as over the top as Carrey's portrayal... if you have not read the books, you may be lost and/or hate the movie. Most people I know who didn't read the books and saw the movie hated it, but my mother and stepfather thought it was good, so really there've been mixed opinions.