I was thinking about this the other day and wanted to summarize what the End Times adds from each book. Please add anything I miss and I will update the original post.
I just did a similar list for the RToB, so maybe this will help:
Nagash:Army lists: Undead Legions
Units: Nagash, Supreme Lord of the Undead (Undead Legions); Mannfred von Carstein, Mortarch of Night (Undead Legions); Arkhan the Black, Mortarch of Sacrament (Undead Legions); Neferata, Mortarch of Blood (Undead Legions); Krell, Mortarch of Despair (Undead Legions); Vlad von Carstein, Mortarch of Shadow (Undead Legions); Morghasts (Undead Legions or Vampire Counts); Valten, Herald of Sigmar (Empire); Crom the Conqueror, Herald of the End Times (Warriors of Chaos)
New rules: Darkest Depths; Haunted Battlegrounds; Lore of Undeath; Armies of the End Times
Glottkin:Army lists: Legions of Chaos
Units: The Glottkin (WoC or LoC); Orghotts Daemonspew (WoC or LoC); Bloab Rotspawned (WoC or LoC); Morbidex Twiceborn (WoC or LoC); Putrid Blightkings(WoC or LoC); Gutrot Spume (WoC or LoC); Festus Empowered (WoC or LoC); Karl Franz Ascendant (Empire)
New rules: Streets of Death; Chaos Ascendant
Khaine:Army lists: Host of the Aestyrion; Host of the Phoenix King; Host of the Eternity King
Units: Malekith, the Phoenix King (HotPK); Malekith, the Eternity King (HotEK); Tyrion, Avatar of Khaine (Aestyrion); Imrik, Crown Prince of Caledor (HotPK or HotEK); Alarielle, Avatar of Isha (HotPK); Alarielle, Incarnate of Life (HotEK).
New rules: Magic of the End Times; Magical Lodestones
Thanquol:Army lists: None.
Units: Thanquol and Boneripper (upgraded)(Skaven); Lord Skreech Verminking (Skaven); Verminlord Deceivers (Skaven); Verminlord Corrupters (Skaven); Verminlord Warbringers (Skaven); Verminlord Warpseers (Skaven); Stormfiends (Skaven); Ungrim, Incarnate of Fire (Dwarfs).
New rules: Realms of the Lizardmen
Archaon:Army lists: The Grand Legion of the Everchosen
Units: Bloodthirsters of Unfettered Fury (DoC or LoC or GLotE); Bloodthirsters of Insensate Rage (DoC or LoC or GLotE); Bloodthirsters of the Wrath of Khorne (DoC or LoC or GLotE); Skarr Bloodwrath (WoC or LoC or GLotE); Skullreapers (WoC or LoC or GLotE); Wrathmongers (WoC or LoC or GLotE); Isabella the Accursed (DoC or GLotE); Balthasar Gelt, Incarnate of Metal (Empire); Tyrion, Incarnate of Light (HotEK); Grimgor, Incarnate of Beasts (Orcs and Goblins); Caradryan, Incarnate of Fire (HotEK); Archaon Everchosen (GLotE).
New rules: Armies of the End Times
Of the new rules, the relevant ones for most games are:
Lore of Undeath: All wizards can now take the Lore of Undeath.
Armies of the End Times (
Nagash): Character allowance raised to 50%.
Chaos Ascendant: Daemons for all!
Magic of the End Times: All wizards know all spells from their lores, lots more power dice, new super-spells for each lore.
Armies of the End Times (
Archaon): Ignore most army composition requirements.