GIMP is kinda odd insofar as for me (who learned to use Photoshop 25y ago) that it (just like every other tool) just seemed cumbersome and clunky with the shortcuts. I couldn't even use German Photoshop because some shortcuts are different. Some other tools were barely usable for what I tried to do, so I think it's unfair to single out GIMP, although the old multi-windowed interface was just something else.

The functionality wasn't even the biggest problem. And JFTR, I'm not talking about anything that came to Photoshop in the last... 15 years or so, I was just slicing PSDs for table layouts and making wallpapers, not actually editing photos like a pro :P