[skillya_glowi]

Well, this is kinda hard to decide since they were all good in so many different ways, but I'd definitely have to say Abe's Oddysee. It just has the distinct atmosphere of Oddworld that no other game could replicate. Not to mention the art -- everything looks so realistic and nothing is out of place.
AE, though, probably is the one for diversity. Gameplay expanded to very different levels, and other possibilites were explored, what with such things as possessing wildlife creatures, Mud emotions, exploding farts, etc. and all.
MO, imo, is on one level with AO in regards to the storyline. Munch is a character for whom you really feel, since he was just a victim of circumstances. But I didn't vote since I really can't decide.