I own both DH2 and Black Crusade... I've already read through DH2 and I'm currently reading BC.

I was wondering: are there any differences between these two systems' mechanics? I've noticed, BC doesn't have the Aptitude system. Is there anything else? Any differences to general rules, combat etc.? Or can I skip these parts of the BC book and assume they are the same as in DH2?

Also, how do BC characters compare to DH2 characters? Are they stronger, or roughly at the same level (at least when it comes to humans - Chaos Space Marines are obviously more powerful than the human Acolytes)?

There are a handful of subtle differences, such as:

-Prices for buying things with 2 ("True")/1 ("Allied")/0 ("Opposed") are slightly different.

-DH2E doesn't have scale modifiers for buying large amounts of gear.

-Rarity modifiers themselves are slightly different.

-Minions and hordes no longer exist.

-Blood Loss is no longer a chance at instant death, but instead a steady time bomb.

-Loads more Lores exist, since everything Common is also Scholastic and everything Scholastic is also Forbidden.

-A few weapon properties, such as Shocking and Twin-Linked, were changed.

-Buying up PR isn't nearly as easy.

-Some talents were consolidated or generalized, such as the two-weapon stuff and those for called shots.

-Fate Points don't have staggered benefits anymore.

-Using psychic powers is more finicky and risky (which suits the mood).

-High-end pieces armor now have Agility maximums.

-Commerce is notably better.

That's what I can think of off the top of my head, though there are likely other things I missed. As for power level, BC characters are unquestionably more powerful by virtue of starting with more abilities/gear and having higher characteristics. (BC humans are on par or slightly better than RT characters, but those systems are not nearly as compatible as BC/DH2E.)

Thanks!

So, the question is: do I really need to read the BC rules before trying to play / GM that game? Or can I assume that the system is, more or less, the same and that the differences are small enough that I won't suddenly realize that something is supposed to work in a completely different way than in DH2?

Also, if I need stats for a Daemonette for a DH2 game (which aren't provided in the main book), could I just, more or less, import them from the BC rulebook?

The rules are not significantly different, though as noted above there exist enough subtleties that you'll want to skim both. What's the plan here, anyway, with crossing over between BC and DH2E? (My recommendations will vary based on this.)

As for importing monsters, grabbing stuff from BC to put in DH2E should work fine except for some of the tweaks to talents. The big changes for creatures between Deathwatch and Black Crusade were in attack styles (full-auto is no longer the end-all-be-all of ranged combat) and Unnatural Characteristics (which are now additive bonuses rather than multiplicative ones). Dark Heresy 2E postdates all that, so you should be good to go after quickly eyeballing things. (BC is a higher-powered game than DH2E but I've seen some of its monsters be just as nasty, so .)

For the power level question, a BC Renegade sits at about 7k experience equivalency I believe, while I would merit a DH2 acolyte at maybe 2k. Not counting starting experience in either case.

@JupiterExile: ah, I see. Thanks, that's an interesting thing to know.

@NFK: there's no plan, actually It's just that I purchased both of these books at the same time and I'm reading them both currently. And I'm wondering whether there's a need for me to read the rules section in BC, if I just finished reading the same section in DH2... Call me lazy

Be aware that insanity and corruption are entirely different animals in BC. A BC human effectively has Resistance: Fear baked in, and can additionally buy Resistance: Fear. They don't get an insanity tracker, but they do pick up nasty RP quirks if they screw up too badly on Fear rolls. And as far as BC is concerned, corruption is a good thing so long as you get it on purpose.