I like two things about Eberron:
1) The new spin on traditional fantasy races. Undead worshipping elves? Devious gnomes? Dwarves who run the banking system?
2) Unlike, say, the Forgotten Realms, there isn't a vast set of lore to the game, so the learning curve for a GM is reduced somewhat. (And it's possible to be a completist without spending an arm and a leg.)