Wow. So...I wasn't sold on the first two books of this series - I would have given them 3 1/2 stars at most - because while they were engaging, there was something lacking overall. The books did live up to the marketing, which is that this is Criminal Minds lite for the teen crowd. I find Barnes to be a very interesting author so All In is the eighth book of hers that I've read. Her intelligence and background in psychology are apparent in every book and although I'm not the biggest fan of her writing style, it's pretty consistent in quality and effective. (Minor note: She likes to repeat certain phrases a lot. A lot. A LOT. A lot!) 
 Anyway, it took two previous books but clearly Barnes really hit her stride with this one and the idea of "all in" is actually pretty apt, since everything is revealed to be connected. There are still a lot of elements that I feel are just too forced and coincidental, which is a big part of the reason why I wasn't too invested in the first two books. However, for the sake of drama and suspense, I suppose that's the only way a series like this would work. Readers will just have to suspend their disbelief as with any TV show - if statistically improbable and rare events like massive ferry crashes, train wrecks, bomb explosions, shootings, various other crashes/accidents, and airplane crashes can ALL occur in a single fictional hospital called Seattle Grace - well, you'll just have to apply the same reasoning to The Naturals series. Every single important character seems to be connected to the overall web of tragic pasts. 
 It's refreshing that Barnes still manages not to overload the reader to the point that it's hard to drum up sympathy for the tragic pasts that pretty much define every character. I felt like the book really hinged on how Lia, as the practical character, more or less delegated everyone's "turn" to have their moment of crisis. At some point you do have to step back and be like "really? could this get more coincidental? is like, EVERY murder from the past 10 years...wait, 50...wait, 200 years all connected?" And did even Cassie's name, aka the significance of Cassandra as the original oracle that got screwed over by Apollo, have to be brought into it too? 
 As I said though, the genius is that Barnes imbues the series with enough seriousness that you're invested in the characters, but doesn't take herself SO seriously that you really can't roll with it - in the way that as a fan, you can still be sad when the characters die in an improbable fashion, while also acknowledging that it's really a forced plot death. Again, very TV (melo)drama in concept. (Disclaimer: I'm not even a Grey's Anatomy fan and I really haven't watched that much of it, but I'm aware of how ridiculous the storyline got...actually, I probably stopped watching because I lost interest after another BS character killing event. GA is hardly the only show that does this, every long running show has eventually pulled out all stops - that poor CSI team ran the gamut from the mundane alcoholism to being buried alive, and speaking of hospitals, a whole lot of improbable events happened in ER too - but GA probably took it to the most extreme.) 
 As a final note, I really wish the book would focus a little less on Cassie and spend more time developing the other characters. The fact that it inevitably turns into the Cassie show is obviously something that Barnes is aware of, given that various characters in the series have called out Cassie for it here and there. However, Cassie still ends up very much a tragically perfect Mary Sue at times, not to mention it's pretty annoying how she always manages to personally come up with just the right clues to solve the case, which feeds back into how very tragically it personally affects her more than everyone else (sorry Sloane! Your 15 seconds of issues are up, it's back to Cassie & mommy!), which leads back to her semi-magically generating the next set clues, until there's a vicious feedback circle going. 
 To me, it's actually all the characters other than Cassie and Dean who are the most interesting. I wish more time was spent on Stirling and Briggs. Yes, I get that this is a YA, but can't the teenagers realistically work with the adults instead of whiplashing between acting like immature teens and master gifted profilers/prodigies/etc. where the actual FBI agents are added in as a last thought in the background? I also think that Lia, possibly the most interesting character out of all the Naturals, gets the least to actually do. She provides the sarcastic scaffolding and maybe her 5 seconds of tragic past personal crisis time, but that's about it. 
 One last thing that I've noticed is that Barnes focuses so much on characterization that she really, REALLY skimps on actual description. Maybe I just have a bad memory but I scoured the beginning of this book to try to refresh my memory on what they actually look like and all I got is that Sloane has blond hair and blue eyes, Michael looks like a rich frat boy or something, Dean is dark and brooding, Cassie has auburn hair, and Lia is...someone with dark hair. Maybe Asian, if I remember right from the other couple of books. A few more "refresher" descriptions here and there definitely wouldn't have gone amiss. I usually like it a lot when authors leave things vague and focus on personalities rather than paragraphs of description about sparkling eyes and meaningless phrases about beautiful souls - an unfortunate hallmark of YA fiction in general - but I could have used a little more than just names and abilities to distinguish characters here.