I finally got Crossed in my hands, after a year of waiting and it did not disappoint. I wasn't expecting too much (it is filler after all) but it does really deliver for me. It's not action packed and the characters spend the majority of their time wandering around the same place, but the new characters and events that happen really made me fall in love with story. The new characters are Vick, Eli and Indie (suitably Dystopian sounding names), and they really add a new layer to the story. I particularly liked Indie, whose character develops more throughout the book and she almost felt like a real person to me. Vick is similar in that he also develops through the story and after telling his past to Ky, also becomes like a real person. 
 The environment itself, is rather barren. This was expected - wandering around the inside of a Canyon was not. Something more desert-like, similar to the Scorch Trials was what I expected but the inside of a Canyon is certainly an interesting idea. 
 Ky's side of the story is a nice touch as well. I'm not if he feels so familiar because Cassia knows him so well, or because his voice is very similar to that of Cassia's. 
 I should mention the similarities between this and Scott Westerfeld's Uglies, as that series is a favourite of mine. Cassia, like Tally, believes in what her society is doing and is looking forward to her future, in the societies grasp. Until a stranger (in Cassia's case, Ky, and Tally's case, Shay) turns up and they see the Society for what it is and escape. Somewhere along the way they are separated and have to find each other again. And of course there's a Rebellion wandering somewhere around the middle of nowhere. I hold the hope that this is just a coincidence, however.