Updated: Aug 11, 2020
Even though it took 6 years for ES6 to be released after the release of ES5, subsequent versions of ECMAScript are released every year until 2018.
ECMAScript 2016 (ES7)
ECMAScript 2017 (ES8)
ECMAScript 2018 (ES9)
Some Important Features released in ES5 are forEach, map, filter, reduce, every, indexOf, getters & setters, parse, stringify, etc.
Some Important features released in ES6 are for..of, for..in, Spread operator, Rest Operator, default params for functions, Template literals, Arrow functions, Classes, Promise, etc.
Some Important features released in ES7 are Exponentiation operator, includes, etc.
Some important features released in ES8 are async-await, padStart, padEnd, Object.entries, Object.values etc.
Some important features released in ES9 are finally() in promises, async iterables.