I have a little experience with roleplaying game design, although none of it is professional (heck, I'm only 16) and one game that I keep on coming back to is one called Purifiers. It is about how the world was once pure, but then demons invaded and now, people blessed by the gods have to use this new power to re-sanctify the earth. The only problem is that once someone has these powers, it is difficult to simply use them for the benefit of man. After all, if one can call down fire from above, then why would one merely use that to kill demons and evil cultists? Man is ultimately self-serving and what greater way to serve self than to use your powers that were a free gift to get all of the power in the world? I already have a bit of work done, and will start a book-page shortly.
Please tell me what you think, and give me what help you can. Out of the geniuses here, I'm expecting lots of great, wonderful, and intelligent advice. What, sucking up has gotten me everywhere in life!

sounds great
Yeah, your idea sounds great... i'm looking foward to seeing it.