In short: Dash & Lily's Book of Dares by Rachel Cohn and David Levithan is a hilarious and delightfully random read. 
 Dash & Lily's Book of Dares was a very quick read, both in terms of page numbers and how quickly the plot and dialogue flowed. It follows Dash and Lily, strangers turned potential love interests, as they pass a red notebook filled with challenges back and forth at Christmastime. The chapters alternate points of view between Dash and Lily, written by David Levithan and Rachel Cohn, respectively. 
 The high point of this book for me was definitely the humour. The characters end up in various hilarious and random situations that must have involved a lot of creativity on the part of the authors. The dialogue was also incredibly sharp and witty. Even small details, easily overlooked by someone reading too quickly, like movie titles and website comment names, were thoughtfully created and wholly hilarious. 
 Some people may be turned off by the extreme caricatures that are Dash and Lily but I found I was able to enjoy them for what they were. That is to say, they were not realistic personalities. Dash was excessively verbose and Lily was very Luna Lovegood-esque. However, I thought their personalities worked for this type of novel. A ridiculous, silly plot requires ridiculous, silly characters to match. 
 I also loved how this book was like a love letter to New York. During the time that the notebook was being passed back and forth, Dash and Lily visit numerous places that I made sure to try and fit in during my recent trip to New York. From Max Brenner, the famous chocolate shop where I bought a chocolate syringe (exactly as it sounds: a syringe filled with liquid chocolate), to the Make-Your-Own-Muppet Department at FAO Schwarz, the famous toy store. And of course, I just had to visit The Strand, the famous book store which boasts 18 miles of books, and was exactly as described in the book, complete with the bookish hipsters who work there. 
 My one major complaint that I had was the timing of events with some of the alternating chapters. During some sections of the book, Dash's chapter would occur on a certain day, while the following Lily chapter would occur the day prior, making the sequence of events a bit confusing. I would have preferred the chapters to flow chronologically. 
 Overall, I enjoyed myself immensely while reading Dash & Lily's Book of Dares. It is the first of the Rachel Cohn and David Levithan's collaborations that I've read (the others being Nick & Norah's Infinite Playlist and Naomi & Eli's No Kiss List). I definitely plan on reading more from these authors.