This was a great beginning, a gorgeously made continuation of the Avatar
universe. The animation was spectacular, feature-quality work, continuing everything that was great about the original but ramping it up. It felt like a Miyazaki film, even more than A:TLA did. Even the 3D computer animation on the cityscape and airships was very smoothly integrated with the 2D animation; the opening shots of the cityscape and the statue of Aang looked like paintings but had 3D movement. The "satomobiles" (cute) looked a little more like digital constructs when in motion, but I guess that's been done for so long that today's viewers are probably used to it, and it's certainly not unprecedented for this franchise.
Korra is a good character, well-played by Janet Varney. She's got a nice strong voice that reminds me of both Mae Whitman (Katara) and Cricket Leigh (Mai). It took me a few minutes to realize it, but in a real sense, Korra is
Aang, or rather the same soul in a new life. And she does have Aang-like qualities in her impetuousness and self-doubt, and in her impulse to heroism. But she's different too, and her difficulty with airbending drives that home. She's a lot more aggressive than Aang, and a lot less polite.
Great to see "Master Katara" again, but it's a shame that Aang, Sokka, and evidently many of the others are gone. That's surprising, really, considering that it's only been 70 years and A:TLA showed us a number of characters who were well over a century old. I guess they wanted to keep the A:TLA characters' presence to a minimum so they wouldn't overshadow the new cast and storylines, but it's still a bit odd.
Oh, and that was wicked of them to tease us about what happened with Zuko's mother. (I think that story's being told in the new comics.)
It's interesting to hear J. K. Simmons as Tenzin; I'm used to hearing him play angrier, sterner characters (J. Jonah Jameson, Generator Rex's White Knight), so I didn't initially recognize him in this softer-spoken role. Although Tenzin does seem to have a Jameson-esque temper boiling beneath the surface. It's interesting... he's Aang and Katara's son, but he takes more after Sokka in appearance and maybe in some aspects of personality (though he's serious, not the jokester Sokka was).
Not sure I'm crazy about the sports focus that emerged in episode 2, but it was well-handled. The climax was entirely predictable, but the execution still moved me.
I still find it surprising that they've gone so quickly from the early-industrial tech of A:TLA's Fire Nation to this early-20th-century environment with cars and electricity and radio and cameras. But then, this is a world where it took them about six months to go from the Mechanist's first prototype hot-air balloons to a fleet of massive war zeppelins. I guess they're just very, very efficient. But I would've liked it if the tech had been a little less advanced, a little more steampunk and bending-based.
By the way, if Republic City is in the former Fire Nation colonies, then Air Temple Island can't be older than about 70 years. So how come there's a 2000-year-old teaching aid there? I guess it could've been moved there from somewhere else, but that line still threw me. (Not to mention that I doubt wooden flats like that could survive 2000 years outdoors.)