Although influenced by Hindu mythology, the game portrays Devas and Asuras as some sort of Villains. (link) They are sent by the gods as they felt the humans were not capable of developing themselves. Humans are known as Gaia in the game.
The Deva represent lightness and creation and the Asura represent darkness and extinction. The powers of the three forces in the game are on expected lines. The Deva have more healing type spells and abilities, the Asura have more damage and curse types. The Gaia (humans) have more physical attack skills. (link)
There is an action packed trailer of Rappelz here. The music is a bit irritating and is used to give an epic dimension to the game.
In the game, Hindu mythology only forms a backdrop, the rest of the action is not associated any Hindu myths. So far none of the popular game creators have made use of the potential of Hindu mythology.
But still it is a good sign especially for Indian gamers and game developers. This can sometimes act as catalyst for more games exclusively based Hindu mythology.