As a 25 year old woman, I grew up on the original ATLA and it took me a while to come to terms with a new avatar. Once I moved past the nostalgia and opened myself up to LOK I was hooked immediately.
I've read other reviews comparing the two and for me it comes down to a few simple things:
This is a DIFFERENT avatar. Just how I can appreciate Aang for always trying to remain peaceful and balanced, I can also appreciate Korra for her hotheadedness. Fact is she is in a world that does not need an avatar and its refreshing to see her character develop throughout the series. (Honestly I would love to see a 3rd series with Avatar Kyoshi which would be a completely different story arch too!) Seriously though, how many times do we want to see the same regurgitated story line where a character has it completely together, knows their purpose and how to accomplish it? This makes the difference with LOK and why I enjoy watching it.
Next, the supporting characters that make up Team Avatar are not master benders. There shouldn't even be an argument here. ATLA Katara was a master after book 1 and Toph is just a bamf from the very beginning. For LOK we aren't dealing with that at all. So sure we can't expect kick ass bending but again, its for taking it for what it is. I feel like LOK makes up with that some seriously awesome fighting sequences.
BOTTOM LINE: I love ATLA, the comic series and LOK. Fans who love the original, who can appreciative 2 different characters with 2 different journeys will love this show as well. It still is it the best animated programming I have ever come across.