I really think that reading Liar first spoiled me for Justine Larbalestier's earlier books. They just don't have the same complexity. I don't think it helps, reading the second book in a series, that I didn't really get into the first book, very much. It's easy to read and pretty fun, but I didn't engage with the characters, and this second book felt even lighter on character development.
The whole Reason and Danny thing... while feeling quite realistic in one way, also seemed to be going way, way too fast, and to be a bit creepy. And it didn't develop their characters -- for me, anyway -- beyond a sort of sketchy outline.
Basically, like the first book, it's fun but somehow unsatisfying, and the problems with slang and so on remain. I am a bit more enthused about reading the third book than I was about reading the second, but I'm not desperately anxious to grab it off my shelf and start right away, either.