For me this really hovers around a 3.5. I did enjoy it, and it's very moreish in terms of reading experience but there were definitely things that I had issues with - especially with more space from the book. 

I did really like that there were twists and turns, but they weren't SO twisty and turny that my brain had to work crazy hard. It was at a nice 'in-between' place between predictable and balls to the wall insane. 

I felt like the ending was rushed, and somehow even though the book was a decent enough length, I feel like I didn’t really get to know the characters as well as I wanted to. I think a lot of time was spent on the island aspect and I wanted maybe a little more with the characters. Sometimes I felt like the description of the island was repetitive.