I really, really, REALLY tried to enjoy this series. I went into it with an open mind, taking the advice of others to not compare it to ATLA and treat it as its own story. But I just did not like it. Sure, the animation was cool, but great animation does not make up for what LOK lacks in plot and character development. Korra herself was an unlikable protagonist, and I found myself becoming ever more frustrated with her stubbornness and unwillingness to change. She didn't even learn from her mistakes; it seemed she stayed the same faulty, stagnant character throughout the 4 seasons.
Also, the writers completely retconned ATLA's original lore and magic. The writers tried so hard to push onto their audience the origins of the avatar, and by doing so, they ruined the magic. The writers of LOK also undermined the original characters of ATLA, perceiving them in a way that completely disregarded the characters' personalities and morals in ATLA.
There are a handful of other reasons why I dislike LOK, but these are my main two.
My condolences for all the other ATLA fans who felt extreme disappointment in this sad excuse for a continuation in the Avatar world. It hurts.