The final in the series, The Book of Fire rounds out the show with interesting and intense battle scenes as well as comedy and drama.
The writers of the show have really mastered their craft with this season. After watching this season, every other show I watch now has
a high standard to live up to. The consistencies within the characters, storyline and animation are unmatched by anything that I've seen.

The Book of Water is a great way to introduce the show. While it can be a bit inconsistent, it definitely finds its craft early on.
This season deals with discovering the Avatar for who he was before he was discovered in ice, the attacks of the Fire Nation and sets a direction for the next season.