ES6 (ECMAScript 2015) introduced major features like let/const, arrow functions, template literals, destructuring, default/rest/spread parameters, classes, modules, promises, and enhanced object literals. These features make JavaScript more expressive, concise, and easier to maintain. ES6 also brought new data structures like Map and Set, and improved async programming. The update modernized JavaScript for large-scale applications. Most modern codebases rely on ES6 features for cleaner code.