Beyond Good and Evil. :P While being in a completely different universe with different characters, it's just as nicely made and just as atmospheric as AO. You'll like it. Plus it's available for pretty much every console that was around in 2003.
Get it off e-bay (search for it on your national e-Bay site if you're not British):
http://search.ebay.co.uk/search/sear...+Good+and+Evil
Or if you're from the UK, you can also find it on Play.com:
http://www.play.com/Search.aspx?sear...d%20and%20Evil
(BTW, shouldn't this topic be in non-Oddworld gaming?)
EDIT: And oh yeah, you can find reviews and stuff for it on GameSpot:
http://uk.gamespot.com/search.html?t...d+Evil&x=0&y=0
EDIT 2: And yes, it's also available for the PC.