Be sure to check out the content on the Learn pages [1], which present a structured introduction to various aspects of the language (as opposed to the blank slate of the Create page). The examples really show off what you can do with F#, even in the browser environment (type providers with IntelliSense, charting, etc.).
That's the first thing I did and that is what makes this an impressive offering. The smoothness of the introduction is very well done and you can easily see how it slowly introduces a novice, which you can easily skip as a more experienced dev because of how well it is structured. A difficult challenge which they've pulled off well.
[1] http://test.tryfsharp.org/Learn