Elder Scrolls: Oblivion - Elder Scrolls were always the forerunners in Open World RPGs, with Morrowind reaching cult status. Then they put out Oblivion, a game with atrocious controls that should have been scrapped after Daggerfall, zero story, atrocious writing, terrible voice acting, moronic mechanics, a cluttered and poorly designed interface and an open world more boring than a can of spam. They did make up for it a bit with Fallout 3, but I still fear for the Elder Scrolls series...
EDIT: If you're about to quote me and tell me how awesome Oblivion is, don't bother. I understand I'm the minority on that one and let's leave it at that.