Mythology is a great place to go looking for ideas to steal for your game. It's even better if the mythology is unknown to your players. On the other had it can be great if it is known to them. There's nothing quite like the "oh shit" look on a player's face when they realize what they're up against. It can also make for a neat campaign. I've run two games set in ancient greece as told by mythology. Monsters, diety intervention. The whole 9 yards. All in all the games were fun.