I have played ET and actually thought it was surprisingly fun. Very simple and broken mechanics at times, but it IS a game and there's some enjoyment to be had.
Aside from that, I typically try to avoid bad games, so it's hard to say. Probably Kirby's Epic Yarn, which barely even qualifies as a game due to the fact that YOU CAN'T LOSE. It's even more of a shame since it was otherwise decent, but the complete lack of consequences kind of removes the point of, y'know, a game.