This is really about 3.5 stars I think, but I liked it enough to bump it up to 4 on here. 
 I thought it was really well-written with some gorgeous imagery and unique and refreshing ideas. The descriptions of the mermaids' fins and the sea and the singing in particular I loved. 
 I felt like Luce, the main character's, voice was a little confused, but possibly this was on purpose, considering how confusing her situation is. I really liked the pacing overall, but I felt it ended a bit abruptly. That was really the only detraction for me. That's quite common with trilogies (and why does everything have to be a trilogy now?), but I have to say I'm definitely looking forward to the next book. 
 (view spoiler)[ 
 The girl's grim lives pre-mermaid and the focus on murder post-transformation really keeps the book realistic and grounded, despite the whole mermaid thing. 
 This book definitely passes the Bechdel test, and the lack of focus on romance is something I really appreciated-- it surprised me how much. I did like the hints of that, though, intrinsic as is it to the mermaid legend. (If the series ends up Luce/Catarina I would not object AT ALL, however unlikely that is.) 
 Overall, I definitely recommend it. (hide spoiler)]