The way it handles separate windows and also network file shares. Even highly-acclaimed managers like Total Commander only support two windows at a time and don't really do customization. When I open ES my first window is my internal storage, swipe right for my microSD card, swipe right for my network drives, and swipe right again for another copy of my network drives. As many windows as I want, in any default configuration I want, with no screwing around with mounting or unmounting network shares. Also the built-in equivalent of SpaceSniffer is quite handy.
Is there something special about it? I'd typically recommend either Ghost Commander or Simple File Manager from f-droid to someone.