Just to chime in with my two cents? You will never get an 'It's too long' complaint outta me.
I'm another of the 'No knowledge of the source material' crowd, and gotta say, the discussions I've seen here do not give me the 'must watch NOW' feeling. You convey the characters nicely, and that's all that matters to me. Unfortunately, as has also been stated, it does leave me at something of a loss in the department of appreciating the rebuilding you've done - BUT, I can say with some certainty that I do quite like them as a cold reader.
As far as this piece in particular goes... well, it has high points, and it has low points. As a background piece, it's beautiful - Korra's first ride in particular was a very enjoyable experience. I must say, however, that I am looking forward to some action in the next piece. Not because this one was slow - I understand that every writer has to do a piece like this every now and again, just to recharge the batteries and provide background for Things To Come - but because, well... -action-. You do action sequences really, REALLY damn well.
Fanboy note time: You and the others are, collectively, one of my three favorite authors. Period. Thank you for the amazing work to date, and I sincerely look forward to more.