I'm going to initially say Action 52, because holy crap, you don't get any more abysmal than that. It's 52 broken, incomplete 'games' that sometimes even won't run at all. Action 52 made me grateful games aren't as horrible as that anymore for the most part. That's kind of why I'm not really quick to jump to saying a game is completely awful anymore.

However, Action 52 is probably an obviously choice to pick, so I'm going to have to say JoJo's Bizarre Adventure: Phantom Blood on PS2. I love JJBA, and I was expecting the PS2 game based on Phantom Blood to be fun; Phantom Blood the manga was really fun and full of action! It would have been perfect and easy to adapt into an action game, especially considering games like Devil May Cry were perfecting the stylish action game genre. The Phantom Blood game, however, ended up being sluggish, dull, and unfair at points. There's actually more dialogue in the game than actual gameplay! Cutscenes take the form of still images with voiceovers that go on for ten minutes. It's just not fun to sit through at all. They were so interested in being as faithful to the source material as possible that they forgot to make the game actually fun.

Apparently, this game was a tie-in for the Phantom Blood movie that came out around that time, but like the game the movie was apparently an awful adaptation as well; so bad that the original author of JJBA forbid the movie from getting a home video release. As a result, The movie is considered forever lost.

I hope one day Platinum Games gets their hands on the JJBA franchise and makes an amazing action game based on Battle Tendency or Diamond is Unbreakable though. That would be awesome.