I recently dove into the 'Descendants' book series after rewatching the movies, and I was pleasantly surprised by how much extra content there is! The books definitely expand beyond the core characters like Mal, Evie, Jay, and Carlos. They introduce new faces from Auradon and the Isle, giving depth to side characters who barely got screen time. For example, there's a whole subplot about Audrey's backstory that adds layers to her villain turn in 'Descendants 3'.
The book set isn't just a novelization—it's a treasure trove for fans. Some editions even include prequel stories about the parents (like young Maleficent and Hades), which the films only hint at. If you're obsessed with world-building like I am, the books make the 'Descendants' universe feel way richer. That said, a few minor movie characters don't get standalone chapters, but the trade-off is worth it for the fresh material.