It's not easy to tell from this document what has changed, but Dr. Axel Rauschmayer does a good job here http://2ality.com/2017/02/ecmascript-2018.html
This specification introduces Async Functions, Shared Memory, and Atomics along with smaller language and library enhancements, bug fixes, and editorial updates. Async functions improve the asynchronous programming experience by providing syntax for promise-returning functions. Shared Memory and Atomics introduce a new memory model that allows multi-agent programs to communicate using atomic operations that ensure a well-defined execution order even on parallel CPUs. This specification also includes new static methods on Object: Object.values, Object.entries, and Object.getOwnPropertyDescriptors.