I completely agree, nothing came close to the awesomeness of Milkdrop 2 in Winamp. That's one of the reasons I got into programming, by being curious about how it "knew" how to move to the music. Still have it installed on an ancient PC, will never delete it!
I still don't get how they did the transitions. Maybe I'm remembering it wrong, but it seemed like one visualisation always smoothly transitioned to another one. No idea how they that worked.
Cool, but it depends on Soundcloud (dying platform AFAIK given the recent exodus). How's that gonna help me if I use Spotify? Spotify can stream to my TV using Chromecast, showing lyrics via Genius. Why can't it also do some VJing? projectM is open source.