I did not actually like this book as much, being that it's about gambling and the mob - both subjects that I thought the author felt out of her depth in. The character of Gemini felt fairly true to form (except I'd have thought the excessive vanity would be more Libra than Gemini). There was a nice little meta touch at the end which I hadn't seen in previous books. And also the twin nature of Gemini was brought out in more ways than one (and that's all I'll say so as not to give away spoilers).
To be fair, I liked the Taurus book a lot more and I do get along better with Taurus people than Geminis. This may actually be an indication of how good the books have been since they're so true to their signs and provoke similar reactions in the reader as one would have to people of that sign.