Book-to-Movie Law states that once you have read the book, you are bound by the media to go see the movie based on said book, and therefor compare to two.
The casting of Diana Agron (from Glee) for Sarah was a good idea for looks, but that girl cannot act. Seriously. The more I see her in things, the more I think I am just not a fan. And the guy who played Number Four, Alex Pettyfer, was way too old looking, I thought. However, these slight annoyances aside, the movie was surprisingly all right. The action was good, the make-up wasn't over-the-top-too-cheesy, and it followed the book quite nicely. Teresa Palmer totally stole the show as Number Six, along with the adorable puppy dog. I enjoyed the soundtrack, which was cranked way up at just the right moments. The whole time I was reading the book I kept thinking how perfectly written for the big screen it was, so it really wasn't much of a huge stretch to make it work. I am impressed with Michael Bay for surpassing my expectations though. Oh, and it was fun to see the trailer for Beastly (also with Pettyfer) on the big screen! Looking forward to seeing that one.
Bottom Line: Book was just okay, and so was the movie. But in this case I think the movie pulls ahead.