This was nicely written for YA novel - the writing didn't feel juvenile at all, it's just a story about teenage characters. So much YA writing is so dumbed down and it annoys me, so this was a nice surprise.
 
However, nothing really happens in the book. They're just flitting around, occasionally trying to find things. It doesn't learn hard enough into the fantasy or romance side for it to be able to carry a minimal plot, so a lot of it felt really aimless. It was just a cute little teen kinda romance and then in the last three chapters BAM, now to defeat the devil.  
 
The villain and their motivation when revealed are very played out - I've seen the same thing 100 times before.
 
Also, a lot of the messages it tries to deliver are done so very heavy handedly - especially towards the end.
 
And OF COURSE

neither Julian or Yadriel remain dead... All I want is a book with a tragic ending, is that too much to ask??

 
Though, having said all of this, the final chapter and epilogue were fucking gold. I shed so many tears. I wish I loved the rest of the book as much.