Finally finished the campaign on Legendary (alone!). Man, those Knights can be a real pain on this difficulty! Anyway, there's always a special Legendary Ending, so I stuck around to see what it is. Let's just say it's one of those things that some will think is super-awesome (like me
), and some will think is no big deal. To see it for yourself complete the campaign on Legendary and sit all the way through the usual post credits sequence. It's tacked on at the very end.
Or you can just search Youtube for it.