I've never read the book so I can't compare them with the series. I can say, however, the series is excellent. I was really expecting something made exclusively for kids, with hokey special effects and poor Disney quality acting. Instead, I was pleased with very talented acting, well written story, and special effects that seemed more real than reality.
Christian Convery, who's been acting since he was in diapers, portrays Gus, aka; Sweet Tooth.
Although Gus is 10, he looks at the world with a sense of innocence and wonder you'd expect from a much smaller child. He sees (Or strives to see.) the good in everything. Gus is not only the first of the Hybrids, he also seems to be the most human among them. Besides his antlers and deer-ears, he's apparently more boy than buck.
Nonso Anozie, who plays Tommy "Big Man" Jepperd, is a force to be reckoned with. He's the reluctant hero on his own quest who ends up being the guardian and companion of Gus. I'm very happy to see Nonso here in this film, playing the more likable role than he did in Game of Thrones as "Xaro," a duplicitous merchant plotting to crown himself king of Qarth.