The story is simple, the idea is original and fun. G rated through out. I'm sure many 8-to-12-year-olds will enjoy it.
I'm still on the lookout for awesome middle grade writing, though. Brandon Mull and Rick Riordan are pretty good, but every one else seems to feel the need to talk down to their audience. It kind of drives me crazy, actually.
I'm not going to continue with the series, but if my kids want to I'd be happy to keep them supplied.