ActionScript 3 has become the first mainstream deployment of an interpreted scripting language with optional strong typing to actually deliver on the performance dreams that have always gone along with that idea.
(The title of this post relates to the fact that ActionScript is a superset of JavaScript. You can still do all of your Flash coding in conventional JavaScript style, if you want to.)
What Flash doesn't seem to have is a true 3D modeling API. People still build their own 3D engines in ActionScript. Which really shocks me. So I wonder if I'm mistaken and there's something more provided in Flash 9.