Dungeon Siege 2. I'm probably the only person who actually played that game and enjoyed it (it really is a very good Diablo clone, even if not much more), but the storyline, aside from one or two small twists, is very, very boring, and the dialogue and voice-acting is just bad enough to be annoying and cringe-worthy without actually being funny or entertaining (in otherwords, it's just bad, not so bad it's good, or so bad it's bad).
While we're hating on Assassin's Creed, the monologues don't sound all that bad, but then again, I stopped playing after a half-hour and never touched it again, after being utterly disinterested in the story and finding the gameplay to be repetitive, mechanical and bland even early on.