I haven't played a lot of games and I may well have played worse that I can't recall now, but the first thing to spring to mind is [a href="http://www.youtube.com/watch?v=kRuhvTAcmJs"]Igor: The Game.[/a] Something my aunt cluelessly bought for herself when she got a Wii for Christmas a few years ago, and which I attempted to play when I cat-sit for her. I had not much else to do and figured, a cute kid's game, right?
God, so horrible. It's often next-to-impossible to tell a playable character from an ITEM you're supposed to pick up at a distance. I mean, it's like the camera is so ashamed to be in the game that it's staying as far away as it can manage. Half the time the smaller characters were like, 1/100th the height of my aunt's TV screen or something. Even at that, it's possible for things in the foreground to get in the way so you can't see what you're doing. You can play for hours (don't ask me why I actually did), and it's just quests for items - half of which the game doesn't even tell you what they're for. The controls feel like you're trying to walk and jump on the moon, the characters repeat the same 3 annoying lines of dialogue from the movie over and over and over, you "faint" for an annoying few seconds of waiting around rather than dying, the small, obnoxious enemies spawn endlessly, and oh yeah - if you make it as far as 1:26 in that video, that horrible "children singing" music? Can't really be turned off, unless you turn off the sound completely. Which means you'd miss any instructions, but since it's all the same "collect X of Y," I guess that wouldn't matter.
I'm sure there's more to the game, but I couldn't bear to play far enough to find out. I'd rather stare at a wall!