At this point most modern games have been mentioned in one way or another, so I'll go with something a bit older:
Gladiators is up there with all time worst playfield designs.
I really like the idea of the shots on the playfield. But anyone who has played one eventually realizes the physical exploit. Hold the upper left flipper up, and endlessly shoot the upper u turn with the upper right flipper. Very easy shot. It will always safely come back to the upper right flipper while holding up the left flipper.
Literally breaks the game and ruins an otherwise very imaginative layout.