I always wondered about Gimp. I use it all the time, but for VERY basic things. But anytime I want to do ANYTHING, even like just add a word to an image or draw a line, I need to go Google how to do it. The newest version seems better, but the UX is just crazy.
As a counterexample to all the GIMP bashing in this thread, I'm using it extensively, don't find its interface crazy and in rare occasions that I use Photoshop or PaintShop Pro I find that my experience in GIMP translates reasonably well.
The point is that a paint application is not something most of us expect to have to spend time learning how to use effectively for the most basic features, because conceptually painting is very simple.
A lot of people expect the simplicity to be the default, and for the complexity to build from that.
A very simple way of making Gimp far more approachable would be to have a "basic" toolbar with a simplified sets of tools and dedicated tools for things like drawing a line, and ask on first startup if you want the basic toolbar or "advanced" toolbars, and tell you how to access additional toolbars.
But there are many other warts as well, such as the Save vs. Export distinction which gives you an error and tells you to use Export if you try to Save with another extension, instead of just bringing up the export options and maybe warning on the first go. 90% of the time when I use Gimp, I have no interest in saving as xcf, and I'd expect that to be the case for a lot of users. Yes, I understand it's worth warning users if they risk losing information, but to then instead telling people effectively "I can see what you're trying to do - it's very obvious, so I'll tell you how to do it instead of doing it" is just annoying.
I never really had an issue on doing anything with GIMP, but in terms of UX i vastly prefer PSP7 which IMO is the last good version of PSP. After many years of using GIMP alone, i reinstalled PSP7 on my PC and i immediately felt much better using it than GIMP (even though GIMP is better on a technical level - faster filters, better alpha support, etc).
I still cannot use Photoshop - or Krita for that matter since they copy Photoshop a lot.
I think one area where GIMP/Inkscape are far better is in the export options. Photoshop & Illustrator barely give you any options for jpeg compression or PNG output. GIMP's JPEG export lets me control color subsampling, optimization, and more. Photoshop just gives me 0% - 100% quality.
It may have been in a different submenu, but the Photoshop JPEG/PNG optimizer was the most powerful/configurable that I've ever seen. Down to letting you configure the palette for PNG.
I looked it up, and it's under "Save for web". It doesn't seem to provide direct chroma subsampling control for JPEG, but the PNG tooling is insane.