to be brutally honest it feels like the cover of a generic (young) children's fantasy book, it's too.. grand and colourful
i think it's also that the protagonist looks so realistically young, Aang was 12 when he came out of the iceberg but he didn't really look 12 and only sorta acted his age for a few episodes, because otherwise it'd be kinda grating to watch as an adult and espically as an older teenager..