I'm a Java programmer and I think classes in JS would be awful. Tacking on the ES6 behaviour will not make JS a sane OO language, it'll make JS a bunch of new, inconsistent behaviours tacked onto the old, inconsistent behaviours.
FWIW I'm with you: I think that treating JS as a functional language is a cleaner fit that crowbar-ing OOP into it.
I think it was a valid approach to the problem and I salute MS for it, but no - I don't like it. We considered it at work and felt we were fighting JS's natural tendencies too much.
Our decision is to deal with JS on it's own terms. Clojurescript would be appealing if it didn't involve an AOT compiler (and one that's not trivial to set up in Windows)
FWIW I'm with you: I think that treating JS as a functional language is a cleaner fit that crowbar-ing OOP into it.