I have been using GIMP for a long time. From my point of view, it is great. I’ve known Paint.NET(PDN) for a long time, but never try it.
And just in May, I tried PDN at last. The feeling is that GIMP will be replaced. It is not because GIMP is not as powerful as PDN, but it is harder to use.
If you want to use GIMP, you have to be familiar with Linux operations custom. The differences between user interface are slight, but the dialog style and manipulation measures are totally different.
For me, PDN feels better.