I've been using ES6 for few months already in our project because we have an ES6 to ES5 transpiler (Babel). There is an unwritten rule now in the team to only use let
and const
. The var
thing never happened 
At the beginning I thought arrow functions were super ugly, but now that I got used to them is fine. You can even omit parenthesis, curly brackets and return
keyword quite frequently. But I think the best part of arrow function is that it implicitly binds this
object so there is no need to specify function() { }.bind(this)
anymore.
Anyway, my favorite one is template strings. We make custom elements so we usually need a lot of strings with variables. This feature is super handy 
If I'm not wrong async/await is actually for ES7, right?