Colfer has a clever and pithy way about his prose that feels reminiscent of Douglass Adams crossed with Terry Pratchett--plenty of droll sarcasm and social commentary without a caustic aftertaste. The characterization is strong, the pacing is snappy, and the variable points of view work effortlessly with the flow of the telling.
Artemis (whose name I still wish was explained, it being far from Irish and traditionally female) is a shakily sympathetic quasi-villain of a character. His intelligence is admirable and his motives, while shady, are at least somewhat justifiable. With his father missing and presumed dead and his mother slipping steadily into insanity, he has been left to his own formidable devices. He isn't cruel or malicious by nature, but he is borderline arrogant and frequently lacking in empathy. It's an interesting and precarious character to be presented with--a genius prepubescent male with worryingly sociopathic potential. It's almost as though he were teetering between either becoming something on the order of the famed Sherlock Holmes... or his guiltless nemesis, Moriarty.
The paranormal aspect of the world-building is an interesting spin on standard fantasy--featuring elves, dwarves, centaurs, goblins, trolls... all under the unifying name of "The People." One of the twists here being that the faerie people are all in hiding from humanity, and remain so thanks to both their inherent magic and the fact that they are technologically advanced far and beyond humans. They also deeply resent that they had to flee the surface world, and hold a generalized disgust for the "Mudmen" who inhabit and pollute their former home. And despite their tech and social advantages, it's clear that there are significant equality issues for faerie females.
My primary hesitation in recommending this book revolves around just how much character development may occur regarding Artemis, and in which direction. The amount of character growth by the end was unclear, though there appeared to be some vague softening of the boy's more criminal inclinations. There's plenty of room here for personal growth and thoughtful introspection for the title character in future installments--but the end of this particular book is pretty open in that regard.
Will Arty mature into a hero, villain, or anti-hero? It's hard to guess at this juncture. But this reader will gladly give another book or two a try in hopes of finding out.
On the whole, this was a promising start to an engaging series.