SPOILER ALERT!
Both the movie and the book were amazing, so amazing they put tears in my eyes at the end, but their were some major differences, and I'm not quite sure which one I liked more. I guess I just want to discuss the differences I remember because they were some really big difference I didn't think were necessary.
1: In the movie Katie's hair is supposed to be brown, but she dyes it blonde. In the book her hair is the complete opposite. It's brown, but she dyes it blonde and ends up telling Alex it's supposed to be blonde. In the movie, she doesn't mention anything about her hair color, I guess she just assumes he'll find out when her roots start to show. I really think they should've kept her hair the same colors.
2: In the movie, Alex's son doesn't care to be around Katie because he wants his mom more than anything, and it creates a problem because he knows his dad is falling for Katie. His attitude is horrible, and he's constantly snapping at his dad and wanting to be left alone. In the book, he really likes Katie and he wants her to become part of the family. He also doesn't have this special tower in his house where his mom used to spend lots of her time (her special place). That area is nonexistent in the book, and Alex ends up just having the letters Jo or Carly-Jo left for him before she died.
3: Right away in the movie, Katie moves to the small town of Southport, North Carolina, and she meets Alex instantly. In the book, she's living in Southport for a few months before Alex even talks to her. She doesn't show interest in him as quickly in the movie, and in the movie they actually sleep together when she does realize she loves him. In the book, I kept waiting for them to have sex, but the opportunity just never arose, though it wasn't needed because Nicholas Sparks expressed their love for one another in a way that made sex seem like it wasn't needed to show just how into each other they were.
4: Katie's husband did not make her a murderer in the book. He simply tracked every step she took, every clue he had until he found her. In the movie, and though she had no idea he even did it until Alex saw the flyer with her picture and confronted her, she was hiding from a man who made her a murderer simply to find her more easily. That fight between she and Alex never happened in the book because she opened up not soon after he confronted her about the similarities he saw between she and the battered women he used to help, and she told him everything about her husband. In the movie, he literally knew nothing until the flyer, until he followed her to the ferry and begged her to come back.
5: Jo was a ghost of sorts in both stories, but in the movie, I never knew her real name was Carly Jo. In the book, Alex talked about his wife quite frequently and always called her Carly, which gave the readers no way to connect her to this so-called neighbor of Katie's. I was very surprised when Katie read the letter Alex gave her because the one in the movie was from Jo, and the one in the book was from Carly Jo. If Alex had talked about his wife at all in the movie, I might've been able to put two and two together, but she just didn't even have a name in the movie. It was as if he didn't want to talk about her at all, when in the book, all he could do was talk about her because he wasn't used to talking about normal things with another woman; he didn't know anything but Carly.
6: The end result was pretty much the same in both. Katie shot her husband and he died. She also discovered, after reading the letter, that her friend was Alex's dead wife. Now why no one seems to think this story is a little messed up is beyond me. Its a completely normal story with no paranormal aspects what-so-ever, and then all of the sudden, a friend disappears and a ghost appears and everything makes a little more sense. It was sweet to know Carly Jo wanted nothing more than to make sure her husband fell in love again, and it was even better to know she wanted to make sure Katie was the woman for her husband. I truly believed this story was a rip off of Sleeping with the Enemy until the twist at the end. Don't get me wrong, it was a great love story with an awesome twist, and that twist made the story so much better because it had a lot of volume Sleeping with the Enemy didn't have.
I can see myself buying the movie and reading the book again. Both were that Wonderful.