Appearances are everything!
Tweaking the visible controls and changing how the interface works.
Thunar has a good set of configuration options that control how it looks. Similarly, most areas of the user interface can be controlled in terms of icon and font size, and there are many smaller options for subtle tweaks.
Thunar’s layout options cover most of the basics you’d expect.
Nemo takes a similar road. The information below a file icon can be controlled, with three slots for this. The list view can have the number of information columns bumped up quite a bit. A few toolbar icons and context menu entries are disabled by default and can be brought into action. Nemo has the bare minimum of configuration options to remove or add something.
Dolphin starts with an understated interface that has a considerable capacity to be reconfigured. When you start to add toolbar icons, you discover that Dolphin has dozens of functions that can be assigned to a visible icon. Regarding file and directory options, there are quite a few choices about what is displayed. So, for example, you can specify that file and directory sizes are displayed as part of the icon view. All the file managers here can sort by different criteria but Dolphin offers particularly detailed options, such as sorting music files by artist or song.
Krusader is an absolute tweaker’s delight, to the point where the sheer number of options can be overwhelming. Some of the configuration pages have multiple tabs. Making these options searchable would be welcome as there are so many. Certainly, if you can work within the two-pane model, there’s little you can’t add to the interface. Unlike the other GUI file managers, it’s easy to alter the colour scheme rather than rely on the system one.
Midnight Commander sticks to a two-panel text-mode interface, but it does offer some options, such as a vertical or horizontal split for the panel, and exactly what is being displayed in the panels and what the format is.