Focus of the Army and the New Book
In the new book, the focus of the army changed somewhat, yet was solidified in other areas. Warriors of chaos have always been a predominately close combat army. They don't really have any shooting and while previously their magic was strong, it wasn't the focus of the army. In 8th edition, with the powerful book lores and emergence of new casters as a result (slaan, book archmages, teclis) warriors moved even further down the magic scale. Now, they still had powerful options (vilitch, infernal puppet) but they didn't match those of other armies.
But enough about what chaos used to be about. What is it about now? The first thing is randomness. Just like the recent chaos space marine codex, which featured a lot of randomess (tables, psychic powers, daemon weapons, possessed, etc) this book features a lot. As it is chaos, it should. Forsaken, which are now a troops choice, roll a d6 every turn and get an either beneficial or detrimental result that will affect them in combat. Every time a character kills a character or meets another criterion, or a warshrine spell is cast, you roll on the eye of the gods table and get a random benefit. Things like mutalith vortes beasts have bound spells with random affects. Some monsters have random attacks. Spawn have random attacks and movement. Giants and hellcannons are random. The lore of tzeentch is amazingly indefinite - the lore attribute, the spells, the spell's rules - none of these are even close to set in stone.
I am usually not a proponent of randomness in a game that is already almost totally determined by the die. But the randomess here is usually good random, not eat yourself random. Plus, you are playing chaos, so clearly randomness is a draw.
Monsters are now a theme. With 2 monstrous infantry units, 2 monstrous beasts, 6 monsters, and a monstrous cavalry unit (not counting lords/heroes) we can create monster mash that the tomb kings can only salivate at. There are mostly combat oriented monsters, but some have other roles.
Combat is still the warriors of chaos main phase. We have what is definitely a stronger magic presence, but you can't rely on magic. Warriors of Chaos, our mainstay core unit, are capable of beating most non elven elites and any core unit out there. Elite units like the slaughterbrute, chimera, skullchrushers and trolls are even killier and more survivable.
Magic. With the book lore prices adjusted for 8th edition, be prepared to not cast everything on 2 or 3 dice now. That said, most everything (save gateway) got much more devastating. I won't get into spell reviews here, but let's say that as of now I am thinking nurgle might be the spellcaster god.
So there is the focus of the warriors of chaos book, and it's strengths. Next I will put up some of the units which made a good impression and those that didn't, but the detailed unit overview will come later.