It may seem kind of expensive, but the first 64 pages are full color and the entire thing is very finely printed. In fact, it's so dense, I wish it were physically larger. Well, it's kind of nice that it lines up nicely with the manga, though.
It's got character guides, illustrations, interviews, episode guides, and more. ARIA fans, even if you're not interested in the animation version, will probably get something out of this. It's physically higher quality than the manga guidebook.
On top of that, it also comes with a special CD drama, which is listed separately under the catalogue number ARIA-2006-03.
