Summary: 7-year-old is sold into slavery to a demon by his father. Learns black magic. Defeats his master eight years later, goes to live with his mom instead, and attempts to return to normal high school life. Of course, it doesn't actually work that cleanly. He's also bad at social and tends to (over)react violently to threats against him or his friends.
Overall, it was well done. Especially considering that apparently it's his first book ever. The characters and scenes mostly leapt off the pages, the plot pacing was excellent, and there was a large amount of impressive ass kicking. (If he has writing weaknesses, fight scenes are not one of them.) The magic system is arbitrary and unexplained, but the author never uses a trick he doesn't introduce ahead of time in some general way, so points for that. My only gripes were a few places where either the plot or the writing felt really clumsy (especially, the Chomsky incident and its immediate aftermath, where it felt like the protagonist was forced into taking the main plot hook rather than actually having a reason to do so) and, essentially, the protagonist himself.
Taken as a contextless character, he's an excellent instance of the edgy chaotic-good dark-but-secretly-white knight with a traumatic past type that apparently every book and movie in a certain genre is trying to exploit nowadays. There's a reason this type is popular though, and the appeal doesn't really wear thin here. But in the context of his specifics... it is really, really hard to believe that a kid taken young and trained in the ways of evil for years and years will, without some kind of major transformative incident, have ended up with the seriously strong conscience, honor, and Good-capital-G alignment that he somehow has. Of course, if the protagonist didn't have at least most of those then the book would be unreadably depressing, so there's an excellent meta reason for it, but sigh. There were a few other character-related irritations too, mostly around how the "Hi I'm a black magic caster" flag in his aura was dealt with, but I suppose those were still well within the YA unsubtlety tolerances. And the love-at-first-sight with the cheerleader was... ehhh. I thought it overplayed a little, but probably that was just because I wasn't fond of her character in the first place.
The morality thing kind of reminds me of the otherwise excellent Timothy Zahn Dragonback books where an orphan is raised by a con artist from the age of three to the age of fourteen, but somehow still ends up with his parents' moral outlook. Because morality is genetic? Though that doesn't help in the case of the Demon's Apprentice, since his father is definitely a complete bastard.