I was leitura zanhar1's artigo link and one thing she said really popped out at me. Here's the quote:

"The main reason as to why I think TLOK gets so much hate is because ATLA was such a great show that por comparison, Korra just doesn't stand a chance. I mean avatar was a masterpiece with unbeatable and lovable characters (to the point where one can even amor the character they hated to some degree!) and a wicked plot. With that in mind I think people set their standards too high. They were expecting something that would blow avatar away or at least match up with the show. And when Korra was just kind of an average show people got upset. Korra isn't a poorly written show, it's just not crazy-good like the story it was spun from."

I think Zanny nearly hit the nail on the head with this one. People had high expectations for this show. As well as expecting LOK to match the quality of ATLA they also expected a show that would give them everything ATLA did. Although I personally believe it is to early to judge the quality of LOK (remember book one wasn't the best in the trilogy either). What people don't seem to get about this show is that it is nothing like ATLA. Something that was an intentional decision on the writers part.

After the conclusion of ATLA the writers made the decision to let the story end there and not return to the world of ATLA no matter how popular the series was. At some point between then and now they changed their mind. Only they know for sure what exactly convinced them to do so, but they did and we got LOK.

Even though they did eventually return the the world of avatar they compromised por setting this new series 70 years into the future that way they were able to get not only a whole new cast of characters but also an almost completely different world to explore and different issues to resolve.

And here lies the biggest difference between the two series. In ATLA the main conflict is external (the fogo lord and his plans for world domination). During ATLA the world is at war. It needs an avatar powerful enough to put an end to the war and lead the nation into a time of peace. The avatar is sorely needed but Aang is not ready to step up and claim the position. Our hero in ATLA excels at the spiritual side of the avatar but is lacking on the physical side. During the course of the series he sees things and meets people that give power and confidence to put an end to his particular issue.

In LOK the main conflict is internal. Sure there's Amon but he is not the true issue in the series. Korra the hero of this series is nothing like Aang from the start she excels at the physical side and defiantly doesn't lack confidence. por her time people have begone to ask, do we even need the avatar anymore? This I believe is the theme of the series. Benders have become less important as technology has given non-benders the power to do things without depending on bending. As benders become less important the greatest bender of them all becomes less important. However the segundo duty of the avatar has become even mais important. The power to make peace. to be the bridge between the four nations. This is an area that to put it as nicely as possible Korra sucks at. never the less this is the skill she must master in order to put an end to her particular issue. Her failings like Aangs put the world at peril and her mastery of it is the central journey of the series.