It's all really down to taste, some people like DX some don't
But the whole idea is to get away from the standard desktop set set my MS, tha standard setup is a background a taskbar (Usually at the bottom) icons placed on the desktop background (either in order or specific places), whic after some time can become a bit boring
DesktopX, is an excellabt way of changing all of the above, in some cases no taskbar (or hidden taskbar), and an animated background (somrthing you mentioned above) with not only fishes, but walking people, skatboarding kiddies, snowflakes, and many more, a great improvement over the default MS desktop
Along with Windowblinds which of course change all elements of a standard MS window, in many cases with skins matching a DesktopX theme, makes for a new and brighter desktop, rhis i believe is how useful it can be, and many people agree it would seem.
Having said all that I refer to the first sentence, DesktopX may not be for all people, I personally use it to impress visitors, some of who cannot believe that I am running MS Windows

, it's really a case of - If you like it, then use it, else just ignore it and don't use it - There are many more exciting products by Stardock, all of which are being improved all the time.
End of speach