I personally think that the greatest thing the writers did was write with an end in mind from the beginning. Three seasons was just right, everything that needed to happen did. But what if another season had been planned from the start (Book 4: Air) (Alright, the last one would be Fire, for sure. Anyway.)? What do you think would have been explored? Any themes you feel were unobserved?

Obviously, Zuko's mother cliffhanger would have been resolved.

I feel that Aang's death at the end of Earth (book 2) would have more lasting effects on the world. I always felt that "the last airbender" was a good parallel for "the last Avatar" in this world. Without an air nation, the cycle has been broken anyway - there will be no future airbender Avatar. Furthermore, Aang did die - I'm watching The Awakening as I type this (first ep of season 3), and he says "I was really gone!" - Kitara's spirit water brought him back, and he did die in the Avatar state, so the established mythology says that the line is broken - plus, they super cheated during the finale of season two by quoting Avatar Roku as saying "if you die, it's over" in the "previously on" segment. They wanted the fact to be fresh in our minds, then didn't do anything with it.

So - let's just say that they decided that bringing him back to life brought the Avatar line back as well. Another mythological fact about the Avatar is that when one dies, another is born - when we learn about Roku's death, we see that the moment he died, Aang was born - was there an Avatar born in the Water Nation, unbeknownst to the rest of the world? That would be super cool.

But I guess that he just didn't die, then. They made it look worse than it was to make it more dramatic.

I was kind of disappointed with how small these huge mythological actions seemed to really be. I was pretty sure that the last standoff with Ozai was going to end in something more dramatic than "he can't firebend anymore." I mean, the sky was all RED and BLUE and RED almost took over and oh I guess one ultimately silly dude can't bend anymore... I thought all bending was going to be suppressed, or something.

Nitpicking is fun, so long as we remember that the show was AWESOME. Incredibly well crafted.