Une bonne photo est une photo que l’on regarde plus d’ une seconde
(A good photo is a photo you look at for more than a second)
Henri Cartier Bresson
A good photo doesn’t go through Photoshop or Gimp, just because it doesn’t run under Linux, but mainly because it’s still a picture, but not a photo anymore.
My photos, which I mainly develop with Darktable (open source counterpart to Adobe Lightroom), are only cut/aligned, if necessary color temperature/contrast/saturation is adjusted and of course sharpened, maybe a sensor spot or disturbing detail is removed.
That’s it, no photomontages (if not explicitly stated) – I personally find graduated filters immoral with regard to the classification of the end product as photos.
Of course, the ideal is to photograph in such a way that you have as little development effort as possible (for me, post-processing is more like Photoshop).