That's... very interesting. I wrote a game like that myself, but the opposite: you gained Corruption, and with each point of corruption, new favors and curses from the abyss. One thing you might consider is letting PCs CHOOSE the ill effects: maybe disad in charisma, but optionally disad in Int or Wis (you're going crazy), or even Dex (you're mutant, deformed). etc. Seems more balanced, since most powers don't seem all that powerful.
Also more flavorful: surely there must be some charismatic demons and devils out there?
OTOH your powers also carry disadvantages, so I dunno.
One think worth considering is what exactly does humanity means. How come these angels/demons are losing HP and capacities. Should they be getting stronger? Also, how is gaining levels helping you become less of an angel/demon and more human?
EDIT: if you want a list of ideas for curses/favors, let me know and I'll post here or PM.