The remake of Pool of Radiance. If you tried to uninstall it from your PC, it would also delete system critical files. So not only was the game buggy, it could wipe our your operating system as well.
Recently, Fable 2 is the buggiest console game I think I have ever seen. Object/enemies stuck in walls/floors. Your dog floating over terain or just through it. Interactive doors that you can in no way interact with. I also had two instances when a gate was supposed to open, but it just didn't. I had to quit, reload and play it again (the exact same way) and it magically decides to work.