Ugh.. Azula. That women should be in therapy. I think she was just deeply unhappy and insecure. I found it to be quite disturbing how she lost it at the end, especially when she was chained. I agree man, I feel sorry for her too.
I saw avatar for the first time as a kid. And back then, I loved every minute of it. But only when I was older, I understood all the symbolism (many references to Buddhism for example), and indeed, all the dark themes. I mean, seriously, Soka was high on 'cactus juice' in the desert, HOW IS THAT SUPPOSED TO BE FOR KIDS? Hahaha!
Blood bending will have a major come back in Korra btw, and it won't be pretty... I've had this really nasty joke with my mates about blood bending... They would make great porn stars. Really bad, I know. Frankly, I think it is overpowered...
If you had to choose one element, what would it be? I'd go for earth or fire, I think. I loved metal bending in particular. Tuff was a badass girl!