This book is great... an Undead version of the Draconomicon. Same format and style (physiology, psychology, analysis of abilities, new creatures, sample specific creature write-ups, lairs, etc). I wonder what will be next in this series?
Orcus gets just 1 page (no picture of him, just his wand), but he is described as a "Death God", with quick details on his temples, domains, rites, quests, etc. There are several other death gods similarly detailed, including Nerull the Reaper and Doresain, King of the Ghouls.
The True Necromancer seems a bit too powerful IMHO. They are similar to a Mystic Theurge, gaining effective caster levels in both Arcane and Divine spellcasting at the same time, except for a few levels where it's just 1 or the other. In addition, they get fairly powerful class abilities at every level. The entry requirements are not really any harder than Mystic Theurge, and True Necromancer goes for 14 levels instead of 10. This means that you can go all the way to 20th level with it after entering the PrC at level 7. Because of the few skipped double spellcasting advances, you'll be effectively a 15th lvl arcane/15th lvl divine caster at 20th level, the same as a Mystic Theurge, but you'll rebuke Undead as a 17th lvl cleric, have a bunch of class abilities (such as Create Undead (a 6th lvl spell) 2/day, Create Greater Undead (8th lvl spell) 2/day, Horrid Wilting (an 8th lvl spell) 1/day, Energy Drain (a 9th lvl spell) 1/day, Wail of the Banshee (a 9th lvl spell) 1/day, and Necromantic Prowess which increases your effective caster level by +4 for all Necromantic spells and abilities, including all of the free abilities listed above! This is just too much, IMHO, and probably makes this the single most powerful PrC I've yet seen. If you restrict it to NPCs, that's fine, but I think it's too much for a PC...