Yea it's defiantly worth it. Once I saw the first season I was so eager to get more. After the second season hit I was instantly hooked. It's now on it's third season and it's still doing a good job of keeping me interested!
Aang was the best imo. After the first series it doesn't really make sense that you watch it, because at least in the first series the elemental powers were needed but now everything is automated, they make it seem like the Avatar is more of a celebrity than a savior.
You should watch it like other said the first season was really good second season was ok it could have been better and they are showing season three right know and I think it is better then the first season.