Unlike Belshazzar and Nebuchadnezzar, Darius doesn't seem to have bad intentions. He probably shouldn't have signed an order making everyone pray only to him for a month, but the story puts the blame for that more on the conniving band of wicked satraps. And hey, at the end of his part of the story, Darius throws the satraps—and, you know, all of their wives and children—into the lion's den. So they end up getting eaten, with the lions joyfully crunching on the bones of various satrap children and satrap ladies. So… that… sort of… makes up for everything? (We're supposed to like Darius. Just go with it.)
Oh, and apparently Darius the Mede wasn't really this king's name, or didn't exist— depending on who you ask. The Bible might be referring to King Cyrus, or another one of the Persian kings.