It took me a while to realize that all the skins are interactive and playable--not just animated. The playlist is the same for all (and includes the llama soundbite), but all the buttons and equalizer sliders work. Really neat (and in-browser capabilities never cease to amaze me).
Glad you enjoyed it! The Winamp player ("Webamp") is open source: https://github.com/captbaritone/webamp