Good, but frightening
I purchased this series for my 9-year-old son, who reads at an advanced level. The characters are very engaging and the plot definitely held his attention (mine, too). It does have a fair bit of graphic violence throughout, and I think the series is better suited to children in junior high or older.
However, the series is very good, and I intend to purchase the rest of the series, since my son has already had exposure to the books and is hooked on the characters and universe.