Just looked at the Valve demo on YouTube and I agree - looks really interesting. I've downloaded the program to test later with my Bamboo.
Reminds me of the old oil painting series with Bob Ross.
*Update*
It's not bad. The fluid dynamics mixing element is useful, but functionally the program lacks what I need. I'll stick with Autodesk SketchBook Pro for now, which suits the way I like to work.