Games that often fail or are just "B" games, even "C" games like CoD, don't achieve legendary status because they fail to implement all of these things wonderfully. You can have great gameplay and terrible story, or a great story with terrible gameplay, but it won't captivate you like the Elder Scrolls series, or even Halo: CE. It takes excelling in all those departments to create a game that will stand the test of time.