Max/MSP is this times a million. check it out if you haven't heard of it. cycling74.com it does the exact same things but with more options, complexity, and a more usable interface. It also has visual fx.
One of the core goals for Overtone is to provide the means for musicians to share their ideas through a programming-language-like notation. This means readability and understandability are at least, if not more important, to expressiveness with the language.
Overtone should be easy to grok, not appear to be some cryptic puzzle.
Strictly Max/MSP/Jitter is a much more encompassing environment than SuperCollider and ChucK, which focus on audio. The advantage of Max is that it combines a great control language with audio programming, a great video matrix library and a dataflow OpenGL API. Generally there are many more 3rd party contributions to Max/MSP than any of the other media programming frameworks with the exception of perhaps vvvv (which is video centric).
That said, the nice thing about all of these environments is that they heavily integrate OSC messaging, which allows you to mix and match anything together. People often combine openFrameworks/Cinder and SuperCollider for instance.