I think, when watching LoK you REALLY need to keep in mind that it was only intended to be a mini-series.
The best part about The Last Airbender, for me, was watching the characters grow and develop. They had three long seasons for that, so everyone was able to get the amount of care that they really needed.
There are some great characters in LoK, but a lot of them get pushed aside because the series is so short. The focus is only put on a couple people, and frankly, I don't like the characters they chose to focus on. Nobody really develops too much throughout the series (in my opinion) and the show feels like it's over already even though there are gonna be more seasons.
However, the animation is fantastic and Amon is a really great villain. The overall focus of the show is on the dark stuff that's going on in the city (as opposed to TLA where there was mass genocide and it wasn't really focused on QUITE as much since the characters were younger), and I really like the steampunk-ish setting.
I'd say it's worth a try, but you really need to keep stuff like that in mind.