Good points, particularly about the story's blandness.
Giving humans the same treatment as every other class--a mix of ability modifiers and special abilities--is certainly a viable way to go. Out of Klaus's list, I like the free feat the best. Single-use abilities and saving-throw-based abilities don't feel right.
What does feel right? Forgive the genre-buster, but for me it'd have to be based on the classic arguments on behalf of humanity, as delivered by Captains Kirk and Picard. I know, I know, but somehow that's what feels right.
So maybe an ability that keys off those speeches, and Klaus's suggestion. Tenacity. An ability that gives a bonus to death saves, or adv on rolls when reduced to less than 1/4 max HP. "humans need conflict, need challenge", "our capacity to feel pain is what makes us human", that sort of thing. Humans at their best when they are pressed the hardest. I could get behind a racial power that reflects that.