In terms of Pathfinder undead encounters, ghosts must be feeling somewhat left behind by the current plethora of fascinating haunts... this product goes some way towards redressing the balance by providing a wealth of options to make ghosts more interesting, more challenging and quite unique.
This is done by presenting a range of powers and a carefully-devised system to enable the creation of specific ghosts balanced for whatever level you need and tailored to the circumstances that caused that particular ghost to come into being. A nice feature is that each power is linked to an example ghost, showing how the power is appropriate to the death of whoever has become the ghost, making the whole thing fit together and make far more sense within the context of the alternate reality in which the game is set.
Mechanically, a ghost gets a power for every three levels of CR it has, with a minimum of one which, to maintain the specific character of ghosts, must be corrupting touch. A few are denoted as being more suitable for the higher-CR ghosts, being ones that can present a significant challenge and so are more appropriate to higher-level parties, a neat touch for those who like to maintain game balance rigorously.
The new powers are quite wide-ranging. Many are further touch attacks or area effects which continue with the concept of ghostly nature by enabling the ghost to exert a malign influence by its mere presence. An example of this is the dead air power, which renders an area around the ghost unbreathable - any creature that enters the area must hold its breath and even worse, if it fails a Fortitude save, the air can be literally sucked out of its lungs! The risk of suffocation becomes very real. The example ghost given for this effect is that of an unpopular miner left behind by his co-workers when trapped in a rock fall. He slowly suffocated, cursing them to his last breath.
The other powers, some 17 of them in total, are in like vein and should prove useful in deigning ghosts that have point and purpose, and which exert baleful effects appropriate to their backstory. A well-considered resource.