I haven't tried windows build, but here's a few things i'm looking for in a pixel art editor:
Mac build
Full keyboard / mouse reconfiguration
Selection tool (drag over image to to pick rectangle areas of image and drag them or move with cursor keys)
Custom pixel brushes (select area and make a brush out of it, with a ui to select/remove brushes)
Native file browser (no foreign/custom file browser ui, should use platform's ui api calls)