I would love to know what other options there are out there. I still use winamp and will keep it installed in its current form but would love to try some alternatives. The winamp highlights for me were:
1) Simple and quick interface on the legacy skin. I like the playlist in particular.
2) Can play old music files from the demo scene is pretty cool, even if it's support wasn't prefect (.mod, .xm, .s3m, .it).
3) Handy disk writer for quick batch converstions to .wav
4) Fast, it used to be one of the best free options for browsing audio samples on windows.
5) A huge array of plugins, most useful to me was the VST adapter that allow me to add professional audio scope visualisation for professional audio.
There have been several detractions:
1) Awful, awful bloatware and bundled crap. (No I don't want 50Mb of crap mp3s, I have my own crap...)
2) The modern skins were historically slower.
3) One of the worst EQs I have ever heard.
4) You had to mess turn off the fade in/out settings and fix the audio buffers to prevent missing bits at the beginning or end of short audio samples
5) Not so good for video, but now I'm just splitting hairs.