Hi,
I have the luxury of having Photoshop but I also have and use GIMP. I recently retired and will have to be more careful now with the $$$. I can see the possibility in the future where I'll let Photoshop go. I can do that because GIMP is so good. Photoshop is slicker and Bridge is really nice but GIMP does the job in a user controlled color-managed environment.
Furthermore; much of the consumer market software out there like iCr*p and Elements, etc. is stuffed with what I call "mangle" features to appeal to the masses. GIMP has a touch of that but for the most part it's well designed to do the job correctly. You can avoid the "mangle" features for the most part but it's annoying that they're there.
I also use Raw Therapee. Again ACR in Photoshop is convenient, but Raw Therapee is its technical equal if not in some cases its better.
So if I woke up tomorrow and had to use only FOSS software I'd say, "no problem," and go straight to work with Raw Therapee and GIMP.
P.S. I also keep a linux (Ubuntuu) system up and running and it hands down swats anything from either MS or Apple.
Take Care,
Joe