WinRAR isn't exactly nice-looking either.
it is to me, haha
probably because i've used it so much
but i took a look at the 7-zip gui, it wasn't as bad as it was when i used it a while ago but it's still pretty damn boring
i like winrar's blueish-gray color scheme and their buttons are just generally nicer instead of those plain shapes
but hey if you like simplicity be my guest.