Conker's Bad Fur Day could probably be considered one of the most immature and freakish games ever made.
It could also be said to be a postmoder work of art and an excellent satire of games and film in general (and cute, Rare style platformers in particular). I mean, the game has you combating an opera-singing pile of shit (literally), an Alien, as well as evil, robotic teddy bears. What does that tell you about conventional entertainment? Conker kicks the crap out of those old-timers, as he damn well should! Ad that to that the surprisingly dark storyline and obvious anti-capitalist themes, and you had one heck of a game.
At least, in my opinion.