Hi Dave,
We are currently playing with your epic boon system, but we made a few changes. I think the changes are something you might want to consider yourself.
The main thing we changed is regarding the 'epic might' boon. This feat is almost mandatory, because you either do half damage (at least as melee) or you don't do damage at all when facing a greater God. Given the huge amount of benefits it gives (AC, saving throws, ability checks, spell DC, damage, etc.) and the fact that you can take legendary actions boon, every character wants/needs this. Therefore, you will most likely spend the first 30-40 points on it instead of taking more flavorful feats. The second problem with the feat is that you need either a high Con or Cha. This makes it much more attractive for charisma-based characters. Even if you just say it scales of only Con, some characters want the option to play a glass canon and because this feat is so mandatory, you basically force someone to invest their points into Constitution. The third and final problem is that taking this boon is better for melee characters as you can overcome resistances and do full damage, but this is not the case for casters as they are limited in both the spells they can cast due to immunity and the spell resistance. We 'fixed' the above three problems in the following manner:
The epic boon feat can only be taken at the following levels (20, 25, 30, 35 and 40). The first time you take the feat is costs 2 QP and the other times 1 QP. You could change the QP cost as you see fit of course. Every character will want to take it at some point, but it doesn't cost that many QP so you are able to get other feats in between. At level 40 you'll be able to fight greater Gods on even grounds, which should be the idea around this level anyway. This also takes care of the ability score problem. We thought about making it 'you need X in your primary stat, but this makes it even more attractive to take and making it scale with Con (which is no primary stat of any class) still makes it much more beneficial for say barbarians and fighters than for shape shifting druids. Making it available at a certain level therefor seems like a more fair way of handling it.
For casters we adjusted the following: taking the epic boon feat also overcomes resistances against spell damage in the same manner it does melee damage. So if you have the 5th epic boon feat at level 40, you'll be able to bypass resistance to spell damage v. Gods. Since this is the same for melee it seems fair. Also, we changed the spell immunity a bit of Gods. Casters are quite limited in their spell selection if they can only cast 9th level or higher spells on a God. We also tried to fix this with epic might. Every level of epic might, reduces the spell immunity of a God by 1. So if a God is immune to 8th level spells or lower and you have the 5th epic might feat, it is than only immune to 3rd level spells and lower cast by you.
This makes it a bit more balanced for casters/melee and you will have some free QP to spend on other boons.
