Worst ever is kind of hard for me since I've been playing games all my life. There were many games I borrowed and returned straight away because of how crap they were back in the NES days. After that, I would buy magazines and pick the most interesting looking games. surprisingly, that turned out very well.
The only game I really hate though is the horrid sequel to the super special awesome SSB Melee, SSB Brawl. HAL mutilated the game play mechanics to appeal to a wider audience and prevent tournaments. They achieved this (actually, they didn't) by killing off combo's, have you trip randomly any time, slowying down the over all speed and kicking all advanced techniques out the door. It basically made Brawl shallow and hollow, even with all the extra features and mini games it still was no where as interesting as Melee.