I have never tried G’MIC until today, but I really enjoyed using it, by playing with the many filters and changing settings, the results were really nice!
One thing I think is missing is allowing the user to keep (or not) the zoom level and image position, this will help to gain more time when you try a new filter. In my case, my PC is kind of slow, and whenever I tried a filter, it took a lot of time to load the preview, and when I change the zoom level it loaded the preview again… The zoom level/position was reset when I tried a new filter. By keeping the zoom level and image position fixed, I can gain a few seconds when I try a new filter.
Thanks