Earlier quoted context omitted.
Basically what I find Koa does for me: http://koajs.com
I am in the Koa boat as well, does Express have anything that Koa does not? (not trying to start a framework flamewar, honestly!)
- server: return something to reply to the browser. Can use `async` for more advanced features.
- express: reply.send() is fairly straightforward. next() for middleware is a new concept but conceptually in the right place (when you are digging a bit deeper in the middleware).
- Koa: yield, function with asterisk, etc.
So I think Koa is fine for devs who have been a while in JS dev, but the learning curve is too steep to get started. Same as what happens with React and the reason create-react-app has become so popular.