Yeah. I was hoping and expecting Amon to be exactly who he said he was. The "solution" the spirits sent to rid the world of bending and the Avatar. I thought that what would happen was Amon would take away Korra's bending, and she'd have lost it. Then there'd be Book 2: "Spirit", in which Korra has to go to the spirits and beg for them to return the Avatar. The whole Book would be about her trying to reach the previous Avatars and the spirit world, all while Amon is taking over the world, without any of her powers (it would also be a nice way to move out of Republic City for the second book and explore the rest of the post-Aang world). The book would reveal why the Spirits decided to abandon the Avatar project they came up with (perhaps this is Korra's own fault or Aang's, or Amon tricked or manipulated them into giving him their power) and culminate with a powerless Korra actually defeating Amon on her own, because she's amazing. Plus, I thought it could be cool if the Spirits returned the Avatar to the world, but not Korra. Tenzin's baby is the Avatar. Korra doesn't get her bending back. That last bit might not work; there's something about Korra's story ending with her finally achieving the Avatar state that works very nicely, particularly if she lost her bending for a whole season and defeated Amon without it. But maybe it would; Aang didn't want to be the Avatar and finally became it, Korra loves being the Avatar and loses it is a nice mirror. Speaking of mirrors, I expect Asami to be a reverse Zuko; I expect her to become bitter and twisted and a villain.
I dunno. I think the problem with Amon is less he's Tarrlock's long-lost brother and that he never took anyone's bending away, but just disguised it through blood-bending. As soon as they pointed out it was all a hoax, I knew they were going to hit the reset button and people could get their powers back. Amon wasn't even scary anymore. So long as Amon actually spirit-bended people's powers away, he could be Tarrlock's long-lost brother and it would've been okay, I mean, the whole "Yakone" stuff worked really well. Great mystery and a great reveal. There was always a sense that Amon was somehow a part of that, that somehow Aang spirit-bending Yakone was a moment that opened the door to Amon's existence. So his relationship to Yakone wasn't the problem. But him being a fraud just killed it.