One of the worst games I've ever played was Bubsy 2. I am one of the few people who thought the first Bubsy was pretty fun. Going back to it today is not the wisest thing to do because it hasn't aged very well, but at least it's playable (IMO).
Bubsy 2, however, is not. It's such a garbled, uncontrollable mess. I have so much hate for it.
Another game that I don't really hate, but that I feel is a pretty bad game is - wait for it - Wizards & Warriors 2: Ironsword. Retro gamers often talk about this game as if it's a "classic" and up there with the likes of Ninja Gaiden, Mega Man or Castlevania. I grew up with these game and hated Ironsword even back then. To be honest, the entire W&W series was always a mystery to me.