Demon: the Fallen is one of White Wolf's most imaginative and enjoyable games! I've read many of their books, and personally I put this in the top 3 alongside Vampire: The Masquerade and Hunter: The Reckoning.
The free-form complexity of acquiring worship and how your character goes about it leaves infinite routes for your players to create unique systems to garner the faith which their characters survive on. Truly phenomenal work, and a joy to read as well as play.
As the other review states, Demon: The Fallen centers on a Christian theme for its source of demonic forces. That's just something you've got to live with, as the whole of the World of Darkness is written around that ideological bent to an extent (except Werewolf, which is my absolute least favorite of their products).