I'd have to say the worst game I played was The Thing.
90% of the time you versed these little head crabs which you killed in one hit but when you versed the large monsters they simply run away as soon as you shoot them.
I remember getting a game that looked so promising but gameplay was like the cross between Frogger, Spyro the Dragon, fruity colorful crickets, and four pounds of crack up your nose, if you get what I mean...
Yeah, it was that bad.