Interesting notes about the premise as reported by the Wall St. Journal (passed on via Last Airbender Fans, as the WSJ link they provide is dead, but I found a working one to the same article):
-It takes place 70 years after Avatar: The Last Airbender.
-It follows Korra, a waterbender and the new Avatar.
-One of the settings (there will probably be many - it's Avatar) is 'Republic City,' a steampunk metropolis melting pot of all four nations that has apparently either replaced or surpassed Ba Sing Se as the center of the Avatar world.
-Not everyone in said city likes benders.
-Aang had at least one child, named Tenzin, who is an Airbender.
If this info is correct (and not misreported, intentionally or otherwise), it means a few interesting things for the Avatar-verse.
-Aang died relatively young, by Avatar universe standards. If Korra is 16 (the usual age for beginning the Avatar journey, and she probably isn't younger than 12), that means that Aang was only around 67 when he passed away. Given that Bumi and Guru Pathik are both well over a century old at the end of the series and still going strong, and Avatar Kyoshi lived for over two centuries, we know that individuals in this universe *can* live an extremely long time by our standards. We don't know the degree to which characters like Bumi and Guru Pathik are anomalous (and Kyoshi certainly was, though presumably the "Avatar Stuff" would apply to Aang). Still, for an Avatar, it seems young. Maybe being stuck in the iceberg did take a toll on Aang's body. Maybe he was killed. In any case, I suspect that there's something going on here.
-Any of the other children and teenagers from the original series could reasonably be alive. They'd be pretty old at this point, admittedly (early to late 80s), but given what we've seen some Cool Old People do in the Avatar universe, all this means is that they'll be more badass than ever.
-Technology continued to progress after the war. I doubt this surprises anybody, but while Avatar: The Last Airbender gave us a world on the edge of a technological explosion, here we see the results. Nature versus unchecked industrialism is going to be even more of a core issue than it was before. Hopefully, as before, both appreciation of the natural world and the utility of new technologies (when used responsibly) will be treated maturely.
-Bending is cultural/belief based, and so, as the influence of technology waxes, the prevalence of bending may wane. The Earth Kingdom had the smallest percentage of benders in the original series (though, given its size, this said little about raw numbers), and was also the most industrialized and bureaucratized (if not the most technologically advanced) nation. Air Nomads, on the other hand, typically eschewed worldly pursuits to focus on the spiritual, and as such, all Air Nomads were Airbenders. It'll be interesting what, if anything, they do with this. The mention of anti-bender politics also suggests that benders have become rarer - they were so integral to daily life virtually everywhere in the original series that it seems unlikely they would be oppressed, but if there were less benders and society did not rely on them as heavily, such sentiments could more easily take root.
-The Shipping Wars will finally be put to an EVEN MORE definitive end. Probably. Unless the series is so unimaginably trollish as not to tell us who ended up with whom via their shared offspring (and probably their offspring's offspring). That said, I guarantee you that people will try to ressurect Zutara in some form with Korra and [most prominent Firebender within 10 years of her age's name goes here]. It's gonna happen.
Now that I've overanalyzed some tiny, insignificant scraps of data, I'll say that I am reserving full-on excitement until we've at least got a little more data. You know, like the front half of Korra's character design.
This is what we're working with so far...
I have about as much faith in Mike and Bryan as it is possible for me to have in a (pair of) creator(s). But not every work lives up to its predecessors, and I've been burned before. I also wish that we could be more certain of Avatar: Legend of Korra reaching completion, but if it's airing on TV, we get no such guarantees. While Avatar: The Last Airbender recieved very good ratings and reviews, it occasionally seemed to be on the verge of disappearance and possible cancellation, and five month periods with no word from Nickelodeon about the air date of finished episodes did not help in the least. Of course, this is part of the gamble any show must make, but animation in the U.S. is a tough bracket to compete in.
This is a lot to worry about now, though. For the moment, I'll be keeping my eyes on Comic-Con to see what spills out.