It might not look like much today, but believe me, when this came out in 2000 it was THE SHIT!
Milko Music Machine was created at a time when most web campaigns were fairly static sites in HTML and banners were gif animations.
This is one of the first true viral campaigns. It attracted 5 million visitors in the first year and peaked at 180.000 unique visitors per day, which was a lot at the time. Since then the concept has been copied many times and it has appeared in numerous books and case studies.