However, I'd argue that the reason most people are adopting CoffeeScript is for the "class ... extends" as it lets them model their JavaScript code much like they might have in their old Java, and more likely, PHP projects. And once you throw that out, the main draws remaining are default argument values, string interpolation, and the ? operator.
The question is, do those benefits warrant the added layer of complexity? Many of us who have worked with JavaScript for a very long time wonder about this, and dread the deeply nested class hierarchies we might encounter in CS projects because CS makes that so _easy_ to do. But bad programmers will write bad code in any language, and I hate to think what a dev who uses `class ... extends` as a crutch would write in plain JavaScript. So, I have both positive and indifferent feelings about CoffeeScript, the only negatives being with the handling of variable scope/shadowing, which is of course opinionated and neither right nor wrong, and the parser itself which makes for ugliness like
window.addEventListener 'load', ->
# Do stuff ...
, false
# leading comma is needed above.