Hero or villain?

Heroism

He brought order to a chaotic empire and didn’t persecute those with different beliefs, which brought him respect, and he wasn’t ousted in a coup.

Villainy

No sources that exist today suggest anything particularly villainous about Darius, although the main source we have is the king himself.

legacy

Darius perhaps should be remembered more, but he is often overshadowed by Cyrus, who came before, and Xerxes, who ruled immediately after him.