will run on any HTML 5 compatible browser
No, it won't. For one, WebGL is not part of HTML 5. For two, HTML 5 is no standard as of yet. For three, IE10 supports HTML 5 quite good, but won't play it.
For four, some browser do support it, but have it disabled by default.
HTML has really gone down the gutter. I don't need no secondary OS in my real OS. Why have the power of 10 years ago today, when I had it ten years ago?
Also, how's audio done if HTML 5 support for it is a complete disaster?
It is interesting from a technical point of view though.