What is notable about the length of the oppression?
Judges 3:8 (ESV)
8Therefore the anger of the LORD was kindled against Israel, and he sold them into the hand of Cushan-rishathaim king of Mesopotamia. And the people of Israel served Cushan-rishathaim eight years.
It is the smallest length in the time of the judges. In later instances, the time before Israel cries out to Yahweh is longer: eighteen (Judges 3:14; Judges 10:8), twenty (Judges 4:3), or forty (Judges 13:1) years.
8 Therefore the anger of the LORD was kindled against Israel, and he sold them into the hand of Cushan-rishathaim king of Mesopotamia. And the people of Israel served Cushan-rishathaim eight years.