Giving the rules a read through this seems very straight forward and interesting. The Nemesis player gets four character choices: Khorne Berzerker, Slaaneshi Damemonete, Genestealer Broodlord, or Eldar Dire Avenger Exarch. Each has their own Nemesis deck of fun things and encounter Imperium forces on the main game board. And of course they may fight the other players.
Actually, any players may now fight each other if they have become an Apostate. This happens if/when your character takes one of the new Apostate asset or relic cards. Fun and powerful, but just a bit on the evil side.
As the man said, "What's in the box?" Let's look.
The Emperor Protects
In all forms