Dishonored itself had a very interesting setting and mythos, and a very clear tone, neither of which were leveraged at all well by the decidedly mediocre plot. None of the good stuff from the backstory gets any catharsis from the narrative (the rat plague is a perfect example of this), and the tone suffers serious whiplash when we're meant to believe that Dunwall goes instantly from unrelenting grimdark in every corner to sweetness and light just because you were a good role model.
I admit I felt the fascinating backstory was under-served by the plot, but I think part of that was intentional - placing the game in a setting in which the character is supposed to be versed, as opposed to making the game *about* the setting. And I didn;t get the grimdark to sweetness and light from your actions - rather, it's the effect your actions have on Emily that lead to the more positive changes in the long run. That said, I do think that was rather rushed in; the moral choice system in the game was generally clunky regardless.
(I think Battuta's alluding to some details one of the writers posted on Twitter, which essentially made the Outsider -- and the fact he's a whale -- into a mythic red herring.)
Except he's not a whale. http://dishonored.wikia.com/wiki/The_Outsider
Unless that's what Batts is complaining about.
I never got the sense that the Outsider was a whale so much as he and the Whales were deeply connected to the underlying fabric of the world. Throughout Dishonored, his powers appear connected to the whales - dependent on them even - but they exist independent of him. The notion of Outsider-as-whale is an intriguing one, but it's not backed up by the original game or its DLC in their entirety. (EDIT: Googling the theory, I see people pointing to the in-game *fictional* book Spirit of the Deep, in which the protagonist of the piece mentions that the leviathan appears as a young man. I never took that book as literally meaning his true form was the leviathan - rather, that whales are physical beings fundamentally connected to the existence of the world and the supernatural forces within and surrounding it, while the Outsider is also dependent on those forces to exist and appropriates their form out of symbolic significance. Think of a conscious God added to the basic magic of the world; the God adopts the symbol of the magic, but it does not mean it actually is part of it.).