They All Fall Down by Rachel Howzell Hall
Then people start dying.
It takes quite a while (about a third of the book) before the first body falls, but once that happens, the book is off to the races. It becomes rapidly obvious that everyone on the island is terrible - living embodiments of the seven deadly sins and they are being punished for the crimes by... someone...
I noticed a number of other reviewers struggled with this book and I can see why. There is a dark humour component to the story that doesn't always land, and since everybody is a terrible person, it's hard to root for any of them to survive. The big "twist" also isn't all that difficult to guess.
I had to take a step back and turn off my brain to enjoy the ride, but it was a fun read.