Conker's Bad Fur Day was developed by Rare and released for the Nintendo 64 in 2001, way past the prime of the console's lifespan.
As most Rare games go, this one's a platformer, but is very violent, crude and vulgar, earning it an "M" rating, one of the few Nintendo games to receive such from the ESRB.
Because of this, Conker's Bad Fur Day is highly sought after by collectors, although very few people are willing to give their copies up. This drives the price of a typical cartridge into the $80-$100 range.
The plot of the game is that Conker, a crude, alcoholic red squirrel, loses his girlfriend when she is kidnapped after a night of heavy drinking, so he sets off on a quest to find her. The gameplay is very reminiscent of Super Mario 64. However, the game earns its mature rating, as there is drinking, swearing, public urination, sexual innuendos and even an opera singing pile of poo for a boss.
The game was met with critical acclaim across the board, from the music and graphics to the gameplay. However, due to its late release, Conker's Bad Fur Day had a somewhat limited production run, but that didn't stop it from becoming a smash hit. It even had a remake on the Xbox.