Movies and The Vow

I haven't seen the movie for The Vow yet and that is because I want to finish the book first. I feel that it is better to read the book first so you can create your own characters in your mind and then compare it to the characters in the movie. You can also compare from the book on what they cut out from the book when making the movie. I did this with the Hunger Games and the book was really good, but the movie was not as good as the book and they cut out important parts in my opinion. I feel that this is how it normally is when they make a movie based on the book. I haven't read Harry Potter,but people say the books are better because they cut major events out of the book. I have also heard this is the same for a lot of the Nicholas Sparks books.