I read the book several years ago. I read A LOT of books like that (first/third person accounts from wars in Iraq/Afghanistan). Lone survivor is hands down the best book in that genre Beyond being a great book, it is a great story on many levels... sacrifice, loyalty, toughness, compassion, and endurance.
I also went to the movie on opening night with a group of friends, some who had read the book, some who had not.
JTH was pretty close:
Some details in the movie are "altered for Hollywood," being different from the book. Some details in the book differ from the official reports. Nonetheless, from what I hear, the important parts of the story, the parts from which we should gather meaning are all true to the spirit of what occurred.
My takeaway was the movie was FAR less moving and impactful than the book, but I don't think they could have stayed true to the book in a 2hr movie.
The above mentioned concepts of the story come through (sacrifice, loyalty, toughness, compassion, and endurance), but the details vary quite a bit. It is a hollywood interpretation for sure.
One of the interesting things I noticed in discussing the film afterwards was that those of us who had read the book, liked the movie less than those who had not read it.
I guess the book was so powerful, the movie just couldn't get there due to the concessions they had to make. While give the book an A, I give the movie a C.