(Spoilers here up to the Battle of Skull Chasm section of Nagash Book I)
One thing I greatly appreciate about the way Nagash Book I is written is how none of the armies involved look like chumps. I've just passed the halfway mark and so far Nagash and his various minions have gone into battle against Bretonnia, Skaven, High Elves, Dwarfs, Night Goblins and more I've probably forgotten. All of this is to built up the Undead Legion and the various Mortarch's leading it but at no point does the opposition end up looking like idiots.
It's an easy temptation to fall into. You're marketing a particular faction, there's a natural desire to make them look great and this can spill over into making everyone else look like pushovers before their awesome might. The last Tau Empire book was quite bad for that, bigging up the Tau at the expense of making the Imperium look weak. It's not just unsatisfying if you happen to be an Imperial player, its dramatically unsatisfying. If the army can just sweep their enemies aside then what's the point of the fight?
We're back to Superman again, really. Peril is a generator of drama, invincibility is not.
This book is Nagash's day in the sun (sorry) but at no point does it make the forces the Undead Legion are fighting look like anything other than genuine threats. The undead will win because this is not only their book but the opening phase of The End Times so naturally the bad guys have to sweep the board.
To take an example: there's a section where Neferata and her Lahmian army fight Night Goblins. Neferata has a huge undead horde including her closest vampire handmaidens, ghouls, Tomb Guard and Neferata herself: the oldest vampire in existence. Her opposition are a mismatched collection of Goblin tribes displaced by her advancing army as she passes through the World's Edge Mountains.
This could easily have been a joke. The first vampire and her handmaidens versus a bunch of short, green, mushroom addicted cowards. Instead the chapter is a pacey little number that sets up the Goblin Warboss as a genuine threat who sets an ambush Neferata walks into through pure arrogance. It was a nice read and from a business point of view it might make people think about doing a Goblin army which is no bad thing because Goblin armies are ridiculously fun.
Actually, there's an earlier chapter where Mannfred Von Carstein takes an army into the Under-Empire and fights some Skaven, a chapter that made me want to dust off my old Skaven army before I remembered I'd actually sold it a few years ago.
(And of course there are the Bretonnia chapters which make me more determined than ever to work on that project, as much as the heraldry makes me want to tear my hair out in frustration every time I notice a difference between the two devices on one side of a knight. I do try to temper my perfectionism but with Bretonnia I find it hard.)
One of the main reasons this book exists, I feel, is to provide inspiration. There are a lot of pages given over to short potted backgrounds of individual characters and units involved in the battles. Any little bit of background can provide inspiration: my Tomb Kings army is based around a character who got a comedy box-out in their Army Book and a single line describing a “Legion of Legend” called the Zandri Blackshields. My first Bretonnia army was based on a name and a heraldry design from the Army Book's colour section.
My only problem, and it is far from unique, is keeping the same inspiration for any decent length of time. I've worked out about three different army lists since starting this book (Bretonnia, Skaven and a Lahmian themed Undead Legion, as it happens). I just have to remember that right now my Tomb Kings take priority.