I borrowed this from Mandy because she said it's a double-excellent book. Personally, I like Inkheart loads more. The Thief Lord is so much less of a complex story...and although the characters are likeable, I never felt like I really connected with them. Added to that, the plot seemed pasted together in places rather than properly flowing.
But, I've read much worse books than this. Maybe it just wasn't Funke's best piece of writing, or maybe I was just expecting something to equal Inkheart. Either way, this doesn't prevent me from reading (and hopefully enjoying) any of her other work.