I really enjoyed On The Edge. The characters of Rose and Declan were well developed and their interactions were highly entertaining. I do love a pain in the ass woman versus a stubborn man scenario, perhaps due to my own tendencies. =) While not really a paranormal romance book, it had just the right amount of it to make the story all the more interesting.
The world Andrews has created is thorough and fascinating. This is one of the more elaborate worlds I've read in awhile, especially considering that it does not feel bogged down with details. I love how Walmart is in the "Broken", appropriate I think. (The scene with Declan at Walmart was very enjoyable as well.) All of the characters are well drawn out, except perhaps the ultimate bad guy. I do not really have any complaints regarding the book except for the fact that while this is a series, each book is dedicated to a different main character. I shall miss Rose and Declan.
Side Note: I found it helpful to picture Declan as more of a Chris Hemsworth (Thor) type rather than the Fabio-esque constipated guy on the cover. I do not quite understand the choice for the cover....if only I was asked. =)