Actualy, to be perfectly honest, I think Demonology can be a bit underpowered.
No, that's not right...
It's not that it's underpowered, exactly, it's that the power you DO get is more than compensated for by the risks of Demonology. But I like this approach to a point... for example, a wizard who trains in demonology isn't going to use it often. Too risky. But it will be something they can DO, if they are pressed into it. And this I like.
But some of it... the possessed prestige class specificly, I think, are actualy too over-compensated. The possessed suffers massive, permanent ability point drain to even be able to use his abilities... doesn't gain any spell levels... can never be resurected, and really doesn't gain THAT much for it... until he reaches really high levels, and can bind some of the really powerfull demons... and demonologists, to be honest, don't tend to live that long in my experience.
Mind you, that part I like. A demonologist puts himself in grave danger whenever he tries to summon a demon. Summoning it is only half the battle... he still has to manage to control the demon. And there are all sorts of modifiers for this... from +s from blood and soul sacrifices, offerings, etc to -s for being unprepared, offering an offensive gift, or having other people around (So no having the rest of your party standing right behind you in case something goes wrong). And a demon uncontrolled is a bad thing (TM).
Generaly most experiences I have had with Demonology have been as a DM, and have ended... tragicly. It always seems like a demonologist tries to push himself too far, too fast... with predictable results. But I'm currently playing a modified Possessed in a friens game, so we shall see how that goes
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