Very weird. Not sure if I like it.
Firaxis history department failed hard not recognizing the fact modern historiography pretty much confirmed historicity of Gilgamesh. Secondly, half of Sumerian bonuses being based on the literary mythological work is absurd, as much as military conquest bonuses. I expected some super early tech, food or infrastructure bonuses for the first civilisation in history, not "hero quest conquest yolo" stuff. Especially as Sumeria consisted of city states that weren't waging extensive conquest wars.
Other than that, the civ looks nice (goody hut bonuses from barbarian camps are quite interesting, Ziggurat is cool) but that's not what I expected from Sumeria so I am disappointed in this regard.