So normally I would say Superman 64, but that would only be judging the only part of the game viewed by most people, the beginning. When you actually get past the first level, the game is more or less decent compared to most other "bad" games.
I'd have to say the worst game I've played is Shrek: Fairy Tale Smackdown on the GBC. My grandmother was notorious for getting me cheap games for my birthday and Christmas when I was growing up, so I have many knock-off GB, GBC, GBA, and DS games just gathering dust, but a GBC rip off of every classic fighting game with difficult controls and horrible music/SFX/graphics just wins hands down. The best would be Casper on GBA, FYI.
Tough call. Either Crystal Pony Tale for the Sega Genesis (too easy) or Silver Surfer for the NES. (too hard) I have heard of other games that look much worse, but I haven't personally played them, so it's not fair to judge them.
-------------------- I bought a cactus. A week later it died. And I got depressed, because I thought, Damn. I am less nurturing than a desert. -Demetri Martin.
I really don't think Super Man 64 is as bad as everyone makes it out to be. It's a terrible game, yes, but it's not 1/10 terrible. Also some of the games you guys are listing (Mario Party 8 for example) are at the very least mediocre. They're anything but the worst game ever.