I think what happened with The Legend of Korra was that people were too quick to set it as the gold standard of animation, and what all kids shows should aspire to, so when the finale was... disappointing, to say the least, people started to realize that it wasn't the shining beacon of television they thought it was.
I was watching The Totally Rad Show, and when they reviewed Tron: Uprising, all they did was compare it to Korra. "It's pretty good, but it's not The Legend of Korra." "I enjoy it, but not the same way I enjoy The Legend of Korra." I'm curious to see how they rate it when they review the whole season on Wednesday, but I'm sure a LOT of people set that show as some sort of benchmark and were let down by it.