This was simply too adorable, funny, poignant, and awesome. I first heard of it on An Odd Blog, and her review here is way better than mine, so go read it! I'm really glad my library had this, because I enjoyed it thoroughly.
Nimona is a shapeshifter who becomes the sidekick to archvillain Ballister Blackheart. The two of them fight against a government organization and its champion, Sir Ambrosius Goldenloin. I'm having a terrible time figuring out how to explain the quirky charm of this graphic novel, which started out as a webcomic. It's steampunky and off-beat, filled with questions about morality and duty and loyalty, but in a fun way.
If This was a Movie, I Would Rate It: PG-13 for violence and some hints that Blackheart and Goldenloin may have been in a relationship at one point. It's very subtext, nothing overt, and should fly over the heads of most kids.