FWIW i'll echo StavrosK experience with PSP (which i used since Windows 3.1 up until PSP7 well into my early 20s... although i distinctly remember disliking it after a specific version - probably 7 - because its circle tool wasn't making perfect circles anymore) and to a lesser extent, WinAmp - and i've tried both again recently. Even though i use GIMP for many years, i still consider the MDI interface, dockable toolbars and the use of the right button as a secondary tool much easier to use than GIMP (which after using it for more than a decade i also know very well and have developed an intuition for how to do stuff with it). Note that i also find Photoshop's (and Photoshop inspired, like Krita's) UI to also be inferior to PSP.

I'm not that particular about Winamp's exact interface, but i vastly prefer audio players with a compact layout that is made up by an area displaying the current song, a slider for seeking, play, pause, stop, prev, next buttons and a floating playlist you can change and hide on the fly.

Oh they were both important programs in their time, I just don't think they were grand monuments to some past golden age of UI/experience. Desktop UI in general was too abstruse for many people to master. Today's mobile touch UI's are much more accessible. PSP and Winamp were pretty sweet if you were a young nerd.