I'd read the book for the first time a few days before watching this movie. All in all, the book was a better story. The movie was fine, and it's enjoyable, but it suffers the same problems movies have when adapting for books. One specific complaint is a competent character (Art3mis) from the book turns into a damsel in distress in the movie.
Watch the movie if you love a decent adventure with plenty of nostalgia, and then read the book if you want a good story. I wouldn't suggest the other way around though.