I don't mind ES6+ syntax. I'd even say that the syntax alone makes for a pretty great developer experience, but I still wouldn't say it's a great language altogether.

I think a fundamental problem with the language is that it's not particularly memory-efficient, and it's hard to make it memory-efficient. The V8 team has done a lot to make it better but they are still limited by the design of the language.

That's particularly painful in mobile where memory is constrained, and on the desktop it's making the typical 4 - 8GB of RAM less and less sufficient. That's important when discussing why Javascript is still an issue when using stuff like Electron and React Native.