I have honestly feel that a void in destiny's story has always been a lack of a main antagonist.
Perhaps someone of great power, or intelligence, guiding the enemy armies like a puppeteer. Taunting you throughout the missions, or revealing troubling facts of people in the tower. Making you question those who say they help the light.
Relatable qualities would be cool as well What if it's a human, or doing it for a cause that is hard to disagree with, but their actions are wrong, ideas like that.
Not to say there aren't any bad guys, or boss fights, like Skolas. It's just none actually speak to you, well unless it's a remark in their language, in which the most you get is a mild translation from an ally.
I would keep my eye on the speaker as well, he says suspicious things sometimes, and seems like a masked villain to me. Maybe they have a plan for future games.
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The darkness...