Cheers, mate.

krita

Looks nice, but is it simplier/faster/more streamlined than Krita?

Oh, this looks actually interesting. I'm not sure I want the 3 million brush configuration options like Krita offers me, so I might try this, though I only do actual wacoming once every leap year and then I quit in frustration.

Also pretty good, lean image editing programs (no focus on actual painting/tablet work):
PAINT.NET if you're on windows. Proprietary iirc, but very good.
Pinta on Linux, basically a paint.net clone.

and here's something seriously insane: https://github.com/serge-rgb/milton
"Milton is an open source application that lets you Just Paint.
There are no pixels, you can paint with (almost) infinite detail. It feels raster-based but it works with vectors. It is not an image editor. It is not a vector graphics editor. It is a program that lets you draw, sketch and paint. There is no save button, your work is persistent with unlimited undo."
(FOSS but windows only atm)
blog entry on how it works: http://s3rg.io/posts/milton_renderer/