Disembodied Voices is equal parts retellings of true accounts and lore from around the world. As such, I found the true accounts far more interesting than the lore, but he covers a wide variety of voices, including those that would compel the listener to do horrible deeds; those that would advise the listener to assist them in a time of danger; and those that would lead the listener in religious matters such as Gandhi, Joseph Smith, or Joan of Arc. There were accounts of voices in the form of small animals calling children outside, wherein they'd lose hours of time and their entire families wouldn't even miss them, as well as ones where a voice would try to lure a person into the woods. To what end? Who knows. Most don't return to tell the tale.
Different lore from various Native American tribes was discussed, as well as some Greek mythology, bits from Christianity, and Irish, Welsh, Icelandic and South American lore, and quite prominently, Hindu ghosts and demons, such as the Rakshasa and the Nishi.
Marczenko focuses on menacing voices, specifically those that use a lure and set a trap in the hopes that their victim will then vanish, typically never to be seen again. Whether the lure includes a helpless sounding young woman or child, a beloved pet or relative, or simply something to tickle the victim's curiosity, such as an incredibly beautiful but dangerous place in nature, it never means something good for the person on the receiving end and there were plenty of stories from years past to explain this.
While I am not as completely convinced as Marczenko is that all of these voices are other-worldly in nature, he makes some good points in his book. I didn't find the history of the lore nearly as interesting as the personal accounts, and some of the anecdotes are so short, I wondered why he included them, but I guess he wanted to present all of the info he found in his years-long quest to discover the nature of the voice that called to him as a child. There were some chilling stories included in this collection and on the whole, I found the content interesting, I just would feel my attention wane when there were long stints of lore from countries around the world. Your mileage may vary, but if you enjoy true "ghost" stories, you may want to check out Disembodied Voices.