Religion should not be forgotten. In the Heian era, many noblemen believed Buddism. So temple were very big and priest had power to the government. Other things are structure and fashion. Structure is original of Japan.
Fashion is interesting material of culture.
Women wore many clothes over and over. It was very beautiful and elegant. Men's clothes were much more simple. The most important point is that these all cultures are original of Japan and they are very beautiful and express Heiankyo very well. I think Heiankyo is very attractive.