All the avatars of Bhagavan are either plenary portions (amsha) or portions of the plenary portions (kalaa) of the Lord.
All of The Avatars appear millennium after millennium to protect the planets from disturbances created by the demons.
But They are not equal to Nand-nandan Sri Krishna as He is the Supreme Lord Himself.
— Sreemad Bhagawatam 1.3.28
The Svarupa or svayam-rupa, Vrajendranandan Sri Govind is the Cause of causes.
— Sri Brahm Samhita 5.1
All twelve rasa (five main and seven secondary mellows or moods) are manifested in their complete form only in Sri Nand-nandan Krishna. So, even though all the manifestations of the Supreme Being are one, the excellence of rasa is only fully realized in the original form of Nand-nandan Sri Krishna.
Source: Dasavatar, by His Divine Grace Srila Bhakti Ballabh Tirtha Goswami Maharaj.
