This is the first book adaptation of a film that I've read and the first I've ever wanted to. There are of course many Star Wars novels, none of which I've read. I wondered what sort of money-grabbing, hastily edited crap I might be delving into. Though in the opening pages there was some awkward language or editing, on the whole those issues didn't persist, and the book gave me what I wanted, which was a sort of "behind the scenes" look at the story, moments we see on actors' faces translated into words, "missing scenes," etc. I got just as emotional reading particular scenes as when I watch the movie and at the same time was interested by some changes or details explained (I believe the adaptation was based on the shooting script).
Some film versus book differences of note:
Unkar Plutt isn't just a jerk, he's kind of a creeper, too. There's a missing scene where he shows up on Takodana for Rey, and Chewie rips his arm(s) off! In addition, Rey comes much closer to selling BB-8 than she appears to in the movie. There it seems her conscience gets the better of her; in the book, she counters Plutt's offer of 50 portions with 100. When he immediately accepts, that's when she decides not to sell the droid; it's like she can't bear to let him have something he so obviously wants.
I'm a bit confused by the timeline of some things in the films, so it was helpful to learn, for instance, that when Kylo Ren removes his mask when Han directs him to, we discover it's the first time Han's seen his son "grown."
There's a whole lot more on Kylo Ren's thoughts and his interactions with Snoke. In the film he comes off as moody and prone to anger. This is actually atypical of him, according to the book. He's all about control and lack of emotion. He even says that revenge is "an adolescent concession to personal vanity," which is interesting given his focus in The Last Jedi.
The book also provides context that I was unclear on, such as the fact that the Republic still exists, but there's typical political infighting in the Senate; most believe Leia is blowing things out of proportion concerning the First Order. In addition, there are more details about the First Order, storm troopers, and how that system-destroying weapon works.
There's more than that, so if you're a Star Wars fan (aren't you?!), it's worth checking out. I've already started the next one (by a different author).