GIMP is too complex (and too slow to startup) for simple image editing tasks.
None of the substitute photo viewer type apps on Linux really seem to stand in particularly well either - I like Shotwell at the moment, but it still lacks an easy to use crop/copy/paste workflow.
gThumb has been my favourite for years for quick resize/crop/rotate/white balance edits and image folder browsing. I don't know why it never was picked as default on Linux Desktops.
None of the substitute photo viewer type apps on Linux really seem to stand in particularly well either - I like Shotwell at the moment, but it still lacks an easy to use crop/copy/paste workflow.