Let's be honest, it wouldn't exactly take much explaining to add a continual game save-type ending, would it? If they're adding a Broken Steel-type DLC then I'll be getting it regardless of the cost but it should have been included without-a-freaking-doubt. Like someone said earlier, at least let me experience some of my efforts/deeds after I've made the big decisions and the story has ended! I got the impression it was going to be a 'big impact ending' but to me it was just a bunch of slides telling me stuff that happens in the near future that has absolutely no bearing on my actual playing of the game (that was hardly shocking nor particularly exciting either).
I'm massively disappointed to say the least. You can, as in most open-world RPGs of this type, spend as much time as you'd like completing quests before enacting that final ending, and easily also keep a. Having known ahead of release that they were going with the definite ending, I've been trying to put off the last quest/point of no return for a while but truth be told, I just like to get the main quests out of the way and explore the world freely afterwards so my patience gave way and I've just finished it (unfortunately). The game designers were quoted in an interview as saying that the main quest's ending was indeed the definitive ending of the story, and that play would not continue beyond that point.