1. The top coolest difference between Alan Dean Fosters novelization and there movie is the way that Starkiller Base works. The fact that it was changed in the movie shows that special effects are a very big seller in three movie industry. In the book Starkiller Base drew dark matter as it's source of power and shot a ball of energy through hyperspace disappearing from it's origin and appearing right outside the target system. To where in the movie it drew its power from the local star. Showing the base draw energy from a sun looks much cooler than drawing from energy we can't see. Io9..com noticed this as well in their article.
2. Kylo Ren is given several changes in the book. Two of the most important changes in the novel are very big hints toward Reys heritage. During the Rey/Ren fight scene Rey loses her lightsaber, Ren and Rey both go to use the force to call the lightsaber to them. The lightsaber flies past Ren and lands in Reys hand. The fight continues. That's the movie. In the book Ren looks to her in disbelief and says It is you! This was probably removed from the movie version because it suggest that Ren knew there was a direct lineage of Luke Skywalker. Rens second change is the way he words his statements when going to kill Han and how he feels when doing it. He really did feel bad about killing his father, showing that he still has light in him also leading to Snokes comment that they have to finish Rens training.
3. Supreme leader Snoke fears Luke Skywalker. In the book it is said in a conversation between Ren and Snoke. Snoke is willing to destroy entire systems so Skywalker cannot be found. Snoke tells Ren that the real reason that the empire was destroyed was compassion. Vader killed the Emperor to save his son. Compassion killed the empire.
4. The end of the book ends pretty much the same as the film. With one exception that mirrors a certain hologram from a new hope......I will let you look this one up its worth seeing and noting the small change. Help me Obi- wan Kenobi your our only hope.