I have been expecting this thread and also wanted to post it but didnīt becouse my ideas were not developed enough. But since it is started ill post what Ive been thinking.
Power based on worshipers, built temples, sacrifices, statues, etc. (as mentioned before)
Habilities like posession, becoming an avatar, sending dreams, plagues, weather control, animal influencing, life seeding, bringing creatures from other planes, etc (this powers should depend of the kind of god like toady says).
Hearing prayers.- A sumary of the most common prayers and the prayers from important NPCs is presented to you seasonally.
Damaging the followers or temples from other gods makes them your enemies.
You choose how fast or slow time passes, adventure mode time if you are to posses a character or send an avatar, fortress mode if you send a plague and seasonally when you just see the world change.
You can loose power if you loose followers, temples, etc. Also if your avatar dies before you come back to god mode (maybe a slow proces) You also loose power if you give powers to mortals.
I donīt like the idea of god points, but canīt think of other way. Maybe there are god points but you donīt get to see the exact number and instead get a description of how you fill and what you can do. You would use god points to manifest your powers.
More later