Full disclosure: I haven’t used it myself much since ~2012 or so, and modern JavaScript now contains many of the most important features that CoffeeScript offered at the time .... Although they did screw some things up (IMHO): null-vs-undefined in default arguments, super as a parent reference instead of a direct function call, optional parens for single-arguments arrow functions (Prettier agrees!), no shared semantics between arrow and normal functions, that class syntax only supports methods and not data as properties, and so on...
When all is done and dusted, I hope that CoffeeScript can be looked back on with affection as a little experiment that showed surprising vigor, one that — with no corporate backing and zero financial support — spread by word of mouth through the web community of the early 2010s, and helped fuel the fire to get JavaScript moving and evolving as a language again.
As a side note — and I write this without bitterness — I do find it a bit strange that extremely well-resourced companies like Dropbox, GitHub, CircleCI, Trello, Airbnb (and many, many more) would write so many hundreds and hundreds of thousands of lines of CoffeeScript without ever attempting to contribute changes or fix the issues that they wanted to fix. It’s open source! They probably would have been able to quickly and cheaply make most of the changes they wanted.
Anyhow, cheers for the blast from the past!