Loving this series, really glad the writers didn't just flop after the last airbender series, this one is fantastic.
My prediction is Amon is actually absorbing people's bending, not just taking it away. The more he absorbs the more powerful he becomes, and Korra's gonna have to master airbending (and the avatar state) as that's the only element he can't absorb in mass amounts, so he'll be weak to it.
I forgot to mention that Amon's hands when "taking away bending" are in a different position to the way Aang's are, and we know Aang is genuinely taking away people's bending, touching the forehead and chest, whereas Amon touches the forehead and neck. I think this implies that there is more to it.