3.5 
 holly is a great main character, pretty cool, intelligent, slightly ocd and funny, although it was hard to picture her as 16-year-old. she sounded too mature for 16 (18 or 19 i would not have had problems accepting it, though). 
 about the rest of characters i don't have a completely made-up opinion, but i can say that i did like dax, james and camille. i did like also the setting in las vegas, even when it is a city i hated as a tourist, it's nice to see other side of it. 
 my only big but with the book is the ending. it felt rushed, not complete, a bit too open for my taste. it's ok to know how holly and dax ended but everything came too quick (and i'm talking precisely about the last chapter).