Not hard to figure out. Don't have to install a bunch of plugins (which are not fully integrated) to do simple things like smudge and dodge/burn.
I haven't tried paint. net but I do like Gimp
It's actually very configurable so you can set it up the way you like.
There is one thing that I would change about Gimp. One.
That holding the ctrl key auto enables "Expand from center."
That gets me ALL the time since so many keyboard shortcuts rely on that key... and sometimes I am busy thinking...
Other than that, I am a fan of Gimp.