Photo Pos Pro isn't as well known as Paint.net and GIMP, but it's another top-quality free photo editor that's packed with advanced image-enhancing tools.
This free photo editor's interface is smarter and more accessible than GIMP's array of menus and toolbars, with everything arranged in a logical and consistent way. If it's still too intimidating, there's also an optional 'novice' layout that resembles Fotor's filter-based approach. The choice is yours.
The 'expert' layout offers both layers and layer masks for sophisticated editing, as well as tools for adjusting curves and levels manually. You can still access the one-click filters via the main menu, but the focus is much more on fine editing.