We're both seen a few of the cartoon episodes but aren't really that up on it (not in the rather geeky way a lot of adults seem to be about it).
Anyway it was fine. The kids adored it and my little 4 year old boy was copying Aang's bending actions throughout and afterwards. It didn't go on too long either.
The plot hurtled past missing out large chunks and with little time for character development (we knew the basic trajectory of it but not the minutiae so this was OK by us). The effects looked great. Music was good and both my wife and I though the 3D worked in quite a good 'field of depth' way throughout.
The dialogue was 'meh' (think the newer Star Wars movies) and Aasif Mandi as the baddie general was a bit off-putting (as he's best known for being a sidekick of Jon Stewart on the Daily Show) but I don't really go to see a kids fantasy film for brilliant dialogue.
We all came out having enjoyed it and looking forward to Book 2.
Whilst it might be a bit fast/shallow/confusing if you've no idea of the milieu and could be really irritating if you are a geeky fan of the animated series, as a holiday kids movie (with popcorn) it ticked all the required boxes.
The film did much better box office than its reviews would suggest so perhaps Book 2 will get made at some point.