Shadow the Hedgehog for the Gamecube. They took everything that was fun for any sonic game, EVER, and gave us a cardboard cut-out character that drives vehicles, walks slower then knuckles, and uses GUNS!!! I ended up giving it to a Nephew for his birthday, and I think doing so may have condemned me to hell.
Also: Worms 3D. It just Didn't transition well from 2d to 3d. The Shotgun became the weapon of Gods because you could use it to snipe people off of plateaus from such distances that the enemy worm was a little black dot with a colored name tag. Sure, it only did 1 damage, but they were still knocked around as if you were shooting them at point-blank range. Bazookas? Even more unpredictable then normal. Grenades? Nearly impossible to aim right. Livestock? Very overpowered. It is a black mark on the Worms series, and I hid it at the bottom of an 10 lb box filled to the brim with LEGO's, and I never speak of it to anybody I know.