Artrage does look very nice for natural media emulation. It's not quite as well known as
Corel Painter but I've heard it's good.
Maybe worth comparing are the free alternatives. The main open-source program I know to actively aim towards natural media emulation in a big way is currently
Krita.
Personally I mainly use
MyPaint for painting - it's not exactly natural media emulation but it's very fast and clean to use which is my main interest - and you can get natural-media-esque results if you really want to.
GIMP itself has much better brushes these days too, you can produce nice results with that although most painters I know either rely on Krita/MyPaint for the brunt of the work, or use the GIMPpainter plugin.
Would be interesting to compare these offerings with proprietary software like ArtRage.
.
Griatch