What's the answer in a short summary other than retro gaming/nostalgia?
If you were into the amiga, this is basically the new Os's of the old amiga for 2011.
AmigaOS 4.1: http://www.amigaos.net/
Sam440/460: http://www.amigakit.com/
AmigaOne X1000: http://a-eon.com/
MorphOS: http://www.morphos-team.net/
AROS Icaros: http://www.icarosdesktop.org/
ClassicWB: http://classicwb.abime.net/