You might like Pinta. It's my favorite no nonsense image editor for basic drawing and quickly changing stuff. Not for big projects, just editing a few pixels, resizing, brightness, cropping, painting, flood filling, basically classic MS Paint but with layers.

It's a fork of Paint.NET, which happens to be my favorite image editor on Windows. The Mono-based port is a bit flaky and crashes sometimes, but the Gimp UX is just unusable for me, so Pinta it is. I tried gimp many times, but I just end up reading forums and often the program either can't do the small stuff I want, or it takes 5 minutes of clicks.