I enjoyed this more than I expected too, coming right on the heels of reading one of the Percy Jackson books, which are okay, but nothing special. (Sometimes the universe just throws books at me in clumps like that. Or, to be more precise, the London public library system.)
This one felt more inventive than the Rick Riordan books, and I enjoyed the playing with fairy legends and weaving them together into something that was very enjoyable to read. I also appreciated that the 12-year-old protagonist was a 12-year-old genius and super-criminal. Artemis still verged a tiny bit on being precious at times, but most of the time, was thoroughly enjoyable as a character.
Artemis, having lost his father in a mysterious boat explosion, and his mother to grief over losing his father, is trying to rebuild the family criminal empire. Being a twelve year old, he is more receptive to ideas that adults might dismiss, and discovers that a) fairies do indeed exist and b) they have a lot of gold.
So he sets out to capture one, but it ends up being part of the elite LEPRecon team, and the first female member at that.
This book wasn't deep, but it did create a sense of sheer enjoyment in the world Eoin Colfer was creating, and the delight of discovery.