I've suggested Exploring ES6 to all my coworkers, and it's my go-to reference for when I need a more detailed explanation of something.
When I picked up Exploring ES6 I thought I already everything, but I actually learned about tons of features that hadn't gotten as much public attention. I'd strongly suggest everyone check it out, even if you just glance over the topics that catch your eye.
Although I am sorry to day the digital version is just too costly. If it was cheaper like most of the books we get for kindle, I would have bought it immediately.