Overall, I really like this book. There is almost enough to work with here and it feels like it's mostly successful. The genre is one that is not often addressed in RPGs and it makes a solid attempt at doing so. I like the variety of new races and some of the new subclasses are things I would really love to play.
That being said, I wish there was more guidance on how to start a game. This is a genre where the transition from concept through character creation to first session is incredibly important and more than a little complicated to get right. The Session Zero section, while it covers the importance of everyone's comfort at the table along with safety tools, is lacking in other advice about getting the game going. Fifth Edition characters are relatively competent, even at early levels, so there's some mild disconnect in figuring out what the PCs should be skilled at and when. The book spends a lot of time emphasizing that Crossing can make you into an envisioned You, but spends very little time with advice for the GM on what that actually looks like. For that, it misses out on a five star rating from me.
So definitely check it out, but be prepared to put extra thought into what your opening sessions look like.