As a casual user on a Mac, I've long since abandoned GIMP for Pixelmator + Imagemagick. Has GIMP improved in usability in the past few years?
I recently installed a fresh version of GIMP (for the purpose of running the exporter script so I can import the layers from photoshop files into the Spine animation tool). I'm only using it as an elaborate runtime for that script, but my impressions are that the UI is basically the same as I remember it from 15 years ago. So, while it's features may have improved, the UI does not seem like it's improved at all.
That's actually a bonus point in my book. If it ain't broke don't fix it. I like that when I start Gimp anywhere I can just start using it. I am not a designer though.