I really loved the themes of the book - about trauma, accepting your darker elements, letting people in, grief, etc. but dear god the plot was so long and boring. I know we all want to know about Nico and will's relationship, they are very cute, but this was too long for this, it should have been a much shorter novel. 

The beginning was really slow and i just don't like humor derived from mispronouncing things and brand names. I also thought the character arcs were pretty obvious. 
Nonetheless, I was very invested toward the end and liked Will and Nico's relationship very much.

Just amazing , it’s a story ultimately about acceptance and it’s just done in such a delicate and beautiful way and just yeah I loved it . Enjoy xx

Okay so I LOVED this book and I was so excited for the release. A book that focused on Nico as an individual (rather than having his own side quest and doing stuff behind the scenes within the main plotline) was an addition the pjo series needed. I'm so happy uncle Rick is giving his most interesting side characters their own development and own series that focus on them as the main character rather than an accessory.
Nico was an obvious (yet very welcome) choice for this development in the pjo universe.
Nico and Will have been beloved characters for a good while within the series and I love how this book draws attention to both the harmonies and hardships of their relationship. It isn't afraid to show how they sometimes clash as individuals but both have an understanding that it doesn't make or break their relationship. If anything: their differences complete one another.
However 
It took me a while to get through simply because it was co-written. And while that wasn't a bad thing nor is it a deal breaker: I'm so used to and fond of Rick's writing style that it was sometimes jarring when Mark Oshiro was writing instead. I know, from friends that have read this book, that it isn't an issue for most people. But to me I found the two authors have different writing styles (especially when it comes to describing settings or emotions) so I sometimes found it hard to get into long reading sessions of this book as the difference broke up the chapters quite a lot to me.
Mark Oshiro was nevertheless an incredible choice of co-author for Rick to make as I did enjoy his individual writing style but I think (since I'm very comfortable with Ricks writing style and I find it easy to read) it simply took longer to read/ follow than a normal Rick Riordan book for this reason