Krita that I have just discovered, and this is an early result of playing around with it. His proportions are a bit out of whack; I didn't do any preparatory drawing and just leaped straight in.
It seems to be aiming for the same sort of niche as is currently filled by Corel Painter, and though it's not (yet) as capable as Painter, it has definite potential. Krita could do with some fine-tuning of its user interface, and its brush design capability, though considerable, is a bit opaque to the casual user.
One point where its textural painting falls down is that the texture is defined by the brush, so if you resize the brush, its texture also gets bigger (or smaller), unlike Painter in which a texture is applied to the "surface" you're drawing on, so it remains consistent even when you resize brushes.
Anyway, I'll be keeping an eye on Krita. My most recent version of Painter is VIII, and I certainly can't afford to upgrade to the current version, so something free and good has definite appeal.