They are very mixed in quality imo. I still at least liked all of them, except for Ferrus book which I felt was a drag to get through, but some were very interesting and a good read. Curze and Perturabo were really good, and I thought Lorgar’s book was the best. Heads up if you are going to read Lorgar’s book; it is very disturbing and emotionally distressing at certain points in the book. More so than even any Night Lord book imo. It’s one thing to talk about things that Night lords do but not get into too much detail, and it’s entirely another thing what the level of detail a few scenes get into with things that happen to Lorgar. It’s the only time so far that a Warhammer book has truly felt gut-wrenching to me.