GIMP definitely suffers from programmer UI design, but Photoshop isn't much better. Menus nested in menus nested in dialogue boxes, keyboard shortcuts that conflict with every other shortcut on any system still in use today, and of course the assumption that everyone already knows what every button does. It's not quite Blender levels of unintuitive, but there's a reason people take courses just to use the damn program. If it weren't for the branding popularity and the fact Photoshop was one of the first programs of its kind, I don't think it'd ever gain popularity with that terrible kludge of a UI, and that's without the ridiculous price.

Ever since GIMP docked toolbars and windows by default (which also took a few versions in Photoshop) I don't think the interface is that bad anymore, at least not compared to Photoshop.