Conker's Bad Fur Day is an absolute masta-peeece! *mwah*
The game is brilliant, with the first half a twisted parody of cartoony 3D platformers (culminating in one of the most memorable bosses in The Great Mighty Poo). Then things get even crazier from there, with Conker visiting Pre-historic worlds, escaping a zombie infested mansion, declaring war against nazi teddiz, and then going full on Matrix on us.
And the multiplayer is soooo much fun. War, Heist, Raptor, Tank, Beach... so many fun modes to play. With awesome weapons (the katana, magnum, and chainsaw were my favorites). It was a huge disappointment when Live and Reloaded messed with this multiplayer perfection.
CBFD is the complete package, and one of the best games of all time!