This book is confusing to give a rating to. The whole world and idea of the book is a great premise, to be able to talk to a ghost and help them solve their death, but there's a few holes in the book which never get fully explained.

Why can Ariel see Joe, and why is (present day) Troy able to see Joe and Joe see Troy? How does Sasha's boyfriend eventually come back into their life, we skip time and it's never explained he just appears when

their dad is found as Joe's killer, he's just there holding her hand.

Why is there so many ghosts in the school? Are they all Joe's classmates and if so why are they ghosts if they're still alive? 

I enjoyed the addition of the side characters especially Lydia, she was developed enough to remind us that she was a living person but not too much for us to know everything about her. I would have liked to see even just one chapter with Gus and Joe's father's perspective, what's going on in their head (either past or present).
The side plots when Ariel and Joe are apart add to the book and give more character to them both, giving light on the idea that absence makes the heart grow fonder but also how sometimes separation for a period of time is needed for both people in a relationship.
Overall a great premise for a book, but not potentially as executed as it could be.