Most of the time, novelizations of films and TV episodes is a bit of redundancy. Most are just prose translations of the script, and add little to the narrative you saw on screen. But they do sell, and at times, can offer a small glimpse into the workings of a script, as things can sometimes change between the end of principle photography and release. Because sometimes, to help the flow of the film along –which works on a linear process- things be changed in a film that are not reflected in the book form of it.
It’s been pointed out that Alan Dean Foster, who adapted The Force Awakens, wrote his book based on an earlier script, so when Episode VII was in post-production and scenes that were filmed but were deleted and new ones shot, some of that could not be changed in the book (which, again, happens a lot as these books are being written while filming is still going on). So while Foster, a prolific writer of his own original science fiction along with a lot of novelizations of movies, wrote a fairly true novelization of The Force Awakens screenplay, due to pressure of getting the book done to coincide with the film’s release in 2015 (though it actually came out about three weeks after), there could be no adds or deletions. Still, the writer is very good and knows his way around the Star Wars Universe, so the book was still good.
With The Last Jedi, adapter Jason Fry (who also has spent many years writing in this universe) was aided by writer/director of Episode VIII, Rian Johnson. This enabled Fry to craft a novel that more closely followed the movie, and because Johnson could not add everything he wanted to the film (the deleted scenes on the Blu ray release show up in the book), it enabled Fry to give them life.
This book does give a better understanding of why Luke Skywalker wants to end the Jedi –even though screenplay does explain this somewhat. The book also gives a reasons why Luke decided to burn the tree that contained the ancient Jedi texts –it was something he planned to do, but Rey showing up on Ahch-To delayed that move. And then we get a better understanding of Kylo Ren and his motivations here. When he hesitated to kill Leia near the start of the film, it was because he felt no anger from her in the Force. And later, as he tempted Rey, it becomes clear that the conflict within Ben Solo –and his justification for destroying the Rebellion, is that he needs this anger to kill them (which is a throwback to both the original trilogy and the prequels).
Also, because the new books in the Star Wars line since Disney bought them from George Lucas, are considered canon, this book explains a bit about Snoke and how he rose to power. Chuck Wendig’s Aftermath series revealed that Emperor Palaptine had a contingency plan just in case the Rebellion proved successful and that the planet of Jakku –isolated, dirty, on the edge of the Unknown Regions of space- would be a perfect place to hide the remnants of the Empire. The book reveals that Emperor Palpatine sensed Snoke through the Force, though he wasn't sure exactly who or what he was sensing. Maybe if he'd learned Snoke's true identity, Palpatine might have taken steps to eliminate him, assuming he saw Snoke as an opponent (which he likely would have). And while the book does not explain where Snoke came from (though again, it’s fair assumption it was somewhere in those uncharted areas of space), it does shed a bit of light on how he became The First Orders Supreme Leader (the computer game Battlefront II explores this a bit).
It is also revealed that long before Luke ended up on Ahch-To, when he was traveling with R2-D2 in search of the remnants of the Jedi, Luke met Snoke. Whether Skywalker knew who he was then is never delved into, but it’s clear that Snoke and Luke (much like Ren and Rey) were Force connected in some way.
All-in-all, a fairly good adaptation of a movie that has divided fans. I can clearly see now why, though, and understand what Rian Johnson was doing with the legend here. Part of it has to do with knowing that the Force is not just connected to the Skywalker family (the prequels laid this out pretty well), but anyone can be Force-sensitive. Anyone.
Plus, obviously, as the franchise begins moving forward after 2019’s Episode IX, it will need to lay the foundation for that expansion in this newest trilogy and novels.