I've played a ton of awful games (intentionally.) Once I tried to beat Superman 64 but got halfway through before it got too broken to deal with, but I did have a little fun. I'd say Rise Of The Robots because there is no room for fun anywhere in that game. It isn't even something you can make fun of. To me, that's the worst kind of game.
Man... People need to play more games if the ones they mention are really the "worst".
It's the same deal with movies. You ask what was the worst and you have people throwing around The Dark Knight, Man Of Steel, and numerous big Hollywood blockbusters. It's like go on YouTube and watch Manos: The Hands Of Fate and not the MST3K version. There's also the stuff so bad that MST3K turned down like The Terror Of Tiny Town and Child Bride. You need to see something legit bad so you can know what bad is and also it gives you a much greater appreciation of those mainstream works that get the blind hate bandwaggons. At least those were well made and had a lot of hard work put into it. Not everyone has to like it, but there are many worse things out there.