I noticed that the fan base and fan activities for Avatar the legend of Aang is still very strong despite the fact that the series ended in 2008. Is nicktoons thinking of a book 4 Air?

I watched Korra too. But it can't compare to Aang. They appeal to very different audiences!

Agreed. They have created a very different look and feel to TLOK, and do not wish to make any comparisons to the orignal series. This show will be made in 4 very short seasons (or "Books") of 12 episodes each. They've been given a chance to develop the characters and hopefully it will get more interesting.