As far as the score goes, it's my favorite of the year. A few words though:
The score doesn't really get many moments during the flick. Narration "gets in the way" and for the most part it's not in your face (for better and for worse). The CD, on the other hand, is phenomenal. The album covers just about all the high points of the movie and is a fantastic audio journey of discovery, enchantment, tragedy and finally action. There isn't a weak track on the album. It's that good.
The only really competition it has for best score is Up, an equally impressive score. Up should probably win as it's more original, but I prefer Avatar because it's an epic.
It was a pretty slow year as far as scores go and I know nominating Avatar for best score might seem like a "just do it because it's the big money maker" move, but the score deserves it.