Quote from SonofZeal
3) Void Suppression. No-save-just-lose for 95% of the monsters out there. Requires a melee touch attack. Spectral Hand is (arguably, depending on your reading) your friend.
2) Moment of Clarity. Grant an ally any feat for a few rounds. Worth noting is that you specifically can't grant Ancestor feats, but Epic feats are, apparently, good to go.
1) Sense Void. Okay, so you can sense stuff anywhere except across planar boundaries, at the cost of a piddly Spellcraft check. This raises a whole series of questions: can others sense you when you're like that? Since you're leaving your body, can you use purely mental actions in that state? Can you move around? How long does it last? Does it count as a divination effect? What can block it? RAW's lack of statement implies very dire answers...
- There's no listed method of detecting if someone else is using this.
- There's nothing preventing the use of mental actions in this state, and there's not even a mention of it requiring concentration.
- There's no method of moving (but see the previous)
- There's no limit on duration given.
- It's never referred to as a divination, nor as scrying, despite the obvious similarities.
- Given that, there's no RAW method I've heard of to block it, short of planar boundaries. Illusions work, though.
In other words, it's potentially "Scry and Die" on steroids.
Conclusion: Void Disciple loses enough spell levels that it could be underpowered, depending on how Sense Void is ruled to work. RAW is vague enough that most of the overpowered potential is based purely on the lack of defined limits. I've personally seen this thing break campaigns though, and I wouldn't recommend it for general PC use.