[Spoiler]Even in defeat...

Amon is a really impressive character. I just want to point out that his only real demise was in his trust for his brother, though I don't think anyone could have predicted that, not even him. Don't for a second think he lost that fight against Korra and Mako. He lost his power with the people when he was exposed, but in all seriousness he could have very easily continued to bring the heat against the new air bender and her companion but realized that even if he won he'd really gain nothing to advance his plans. He chose to retreat.

That guy is absolutely insane when it comes to power and probably could have killed Korra, her friends, and any other group of people short of Bumi's fleet in whole. Even in defeat, he had a plan to retreat with his brother and would probably have come back with a vengeance in a few years time when the next avatar would only be a toddler. I'm sure the reason Tarrlok did what he did was because he knew of Amon's power and this was the only way to end his threat permanently.

He was quite possibly the most powerful person alive short of an avatar in the avatar state.