It sucked me in but it does have a lot of violence including gangs, slavery and attempted genocide.

Have you read the Grisha Trilogy? This is a spinoff series (I think); as much as I enjoyed it, I think maybe I should have read Grisha first.

Never read this author before, no.

This is the only one I've read by them. Other booklikers said not necessary to have read the Grisha trilogy first -- I'm not sure if it would have changed anything for me. (Although I'm definitely going to read it now).