One of the most common criticisms I hear of Black Crusade, is that you "can't" play as one of the original Traitor Legions, as your character starts off as far too puny for a ten thousand year old veteran. Now this isn't something I personally have a problem with as I'm very much a do-it-yourself gamer, if there aren't any rules written, I'll write them myself. However, I'm glad that we're going to get this level of detail for Black Crusade.
FFG look to have struck a nice balance between making a Thousand Sons different enough from a Sorcerer from the main rulebook, without making them too powerful. For instance, although you generate a character with more psychic powers and equipment than a normal Sorcerer, you also start with more Corruption. You also start with a normal number of wounds and toughness rating, making you just as squishy as any other character.
I'm really looking forward to seeing what else Tome of Fate has to offer, FFG have mentioned Daemon Engines and new psychic powers, but hopefully we'll get some new minions and adversaries too.