Ok so you want to play a Chaos cultist, why? Now i'm a long time Vampire player (since first edition) and enjoyed it a lot. However Vampire and i would guess Black Crusade (keep thinking of My Chemical Romance for some reason) have the potentiaal to turn into a moustache twirling exersice or a exersice in evil for evils sake. I am not saying this is a bad idea i'm just opening that debate so here we go.
So lets look at this, at it's best the good things are the potential to view the 40k universe from a different perspective, play a complex character in a complex setting. There is the potential to play some mind blowing scifi/supernatural senarios (i'm thinking anime here!), politics, soul seaching, looking at the chaos gods in broarder strokes and exploring the human condition, what is freedom, and in serving the gods are you exchanging one form of servatude for another. Also who dosn't want to be the bad guy form time to time. I think the Fluff will be awsome if it is as good as the old lost and the damned books. Playing the mindset of someone who worships pure chaos and it's effect of their personality looks huge fun! A party of fully developed characters and a good gm this would be great!
Now lets have a look at it from the opersite direction it is a game that allows you to play a diesised, murderous, manipulative sexual sadist with Kewl powers engaged in terroist acts against humanity in an atempt to sell humanitys to evil gods ... see what i did there? Now at it's worst it becomes D and D with some serious issues. For those of you in the UK see this book in the Daily Mail soon You can put the same spin on DH (torture) RT (greed is good) DW (ultra violence). The problem is i have played enough rp games with people playing 'evil' for evils sake and it is either to camp for words or makes you wonder if your mate needs some proffesional help, don't even get me started on LARP evil! The main problem is that people don't view themselves as evil they act, normaly with best intentions, no matter how skewed they are and with a bad DM and group it could esialy slip into combat, camp evil and torture porn.
Alot of what will happen with this product will be how it's presented and play tested. WIll it be mainly about Chaos undivided? are the playtesters all grown ups who roleplay alot (if so it might be worth inviting players who are coming form D and D to see if people will get the vision for the product form the book) and what is the intention behind the book? Now white wolf might have done some of the most pretentious RP supliments in history (banging on about Joseph Conrad etc!), but they did, in the early days at least, make it a antiHERO game.
Anyway please don't look at a crisism and look at it as a open dialogue. Anyway i'm off to put a black cape and hat on and cackle evily until the other half puts me back in my place!