It seems that nowadays, a large majority of the movies being made are adapted from books. However, I don't believe that there has even been a movie that has followed a book word for word, plot line for plot line. Surprisingly, though, I am not here to complain about that. I understand that it is often necessary to make changes to stories when adapting them to movies whether it be due to logistics, money, or even just director/screenwriter creativity. Like I said, I'm not here to complain, but I do have some comments on this phenomenon.
For the sake of context, I'm going to list some successful movies that were based on books. Movies such as "The Hunger Games," "Die Hard," and all of the "Harry Potter Movies" are some of the very many movies in this broad category. And for all of these movies, I can name distinct changes that were made.
Of the most obvious sort, "Die Hard" was adapted from a book by the title of "Nothing Last Forever" where the main character was named Joe Leland, as opposed to the movie's John McClane. So, not only did they change the title, but they changed the name of the main character. Why this was done has to do slightly with contracts and all that jazz, but at the same time, it seems very unnecessary, especially because they kept the general plot very similar. It's needless to say that this was a very loose adaptation, and the movie was incredibly successful. (Side note: just because this movie takes place on Christmas Eve, does not make it a Christmas movie).
Another type of change that directors and screenwriters alter when it comes to movie adaptations is the deletion of characters that seem significant in books. An example of this would be the removal of the not so friendly poltergeist Peeves from the "Harry Potter" movies. This is something that annoys a lot of fans, but to be honest, the movies are still good without him in it, to the point where his absence is not strongly noticed. I will admit that I wish he would have been featured in the movies because I would have loved to see that character come to life on the big screen. However, this did not happen and the movies clearly did not suffer because of it.
Taking away characters isn't the only thing done. Movie makers often alter certain parts of the plot line that seem entirely important. Let's take "The Hunger Games" series for an example. In the books, after their first time in the arena, Katniss and Peeta both escape with significant injuries. Katniss is deaf in one ear and Peeta has to lose his leg. These injuries are soon fixed by the Capital's doctors, making it so Katniss can hear again and so Peeta now has a prosthetic leg. Did these instances occur in the movies? Nope. Were the movies still good? Yep.
My point in all this is, yes, movie makers mess with the books they are adapting to the extreme. They squish and squash the plots and characters that we readers grew to love, whether that be through flat out removal, sequence alterations, or writing a movie that basically is completely different and giving it the same title *cough* "Percy Jackson" *cough*. But those factors alone don't make the movies bad. The thing about movies and books is that they are two completely different things, so that means they need to be appreciated differently, even if they are drawing on the same story.
Changes from books to movies can definitely be irritating, but that doesn't diminish the worth of the movie. I am an obsessor when it comes to both books and movies. I love to see what directors put on the screens to represent my favorite characters and stories and obviously, they are not always as I pictured, but (if the movie is still good) I appreciate it for what it is, not for what it may or may not have gotten wrong.
In summary, read lots of books and watch a lot of movies and love them both because they are both magnificent works of art.