So my college buddies and I played a campaign of Dark Heresy recently We are not playing as marines, but rather a group of human heretics. To make sure we could kick off, we got together online one weekend and started making our characters.
So aside from the typically "Khorney" names that GW tends to have in their fluff, here are my thoughts on the game as gleaned from character creation
1- The game is very rich. There are alot of skills and talents and items of wargear. I as a Tech guy have a Servo-arm, utility mechadendrite, ballistic mechadendrite, internal grav coils, and some other cool Machine tech. I was able to upgrade my weapons in various ways, had a vast array of weapons to choose from. But all my friends were very easily able to define their characters in their particular path from the get go. There is really no awkward start up phase.
2- It is very accurate to the lore. Everything is based on or entirely conceivable in the 40k universe. Alot of research and dedications was put into this book, and all the "Tomes" that support it. I think these guys at FFG may be more knowledgeable than some Black Library authors now.
3- It feels chaotic. The blessing of the gods tables are just as likely to ruin you as bless you, and the infamy and corruption mechanics that go into determining these are pretty neat, but require a good GM to run properly IMO.
1- Poor layout. You have to flip (or scroll if digital) back and forth a million times during character creation to reference different things. Certain things aren't even in the character creation chapter, like movement and weight capacity. We spent a whole 3+ hour session on just character creation. I had 4 copies of the pdf open at one point so I could easier switch between pages to reference what I needed to.
2- The character sheets are missing vital skills/talents. Things like survival just aren't on there.
3- Difference in language between the character sheet and book. So when you look in the book for skills/talents it defines them as Known, Trained (+10), Experienced (+20), and Veteran (+30) where as on the character sheet it goes Trained, +10, +20, +30. Easily able to realize what it means, but it just a very annoying inconsistency IMO.
4- Initial equipment procurement is BROKEN. This is easily abused. I was able to get a servo arm added to my Heretek, which proved invaluable in the long run and was our MVP. That is right, a mechanical arm was the MVP.
Now, the game as a whole can be really fun, but it is really easy to break. If you avoid using the tomes, I don't think it would be as easy, but once you dabble in those, your GM will have to keep a tight leash on the game to run it smoothly. That said, it is still highly possible to make a WAY OP party.
Rules As Intended vs Rules as Written that covers this pretty well
"Let me give and example. I just finished a Black Crusade game that only lasted 5 sessions. We had already made our characters WAY more powerful than they should have been via clever use of equipment procurement and talents (we had +8 to our initiative and I myself was +10. To a d10 roll. I was ALWAYS faster than the maximum the dice could give). We had a nurgle psyker in the group and a slaaneshi flesh moulder. One of the things the flesh molder could do was boost a characteristic. SO the psyker had him boost his willpower, already a considerable 60/100. Because of the talents between them, and the bonuses to the ritual they performed, and the flesh shapers already considerable skill in his art, they were able to pass the check required to improve his willpower by 5 degrees of success, giving the nurgle psyker a 110 willpower, which meant AUTO SUCCEED ALL TESTS. When the GM decided that this was to broken of a way to do that, the psyker's player INSTANTLY had a plan be which involved possession of himself and then using his already considerable willpower and bonus to force the daemon into submission, the end result being he had a will power of 110. So at the end of the session, we all concluded the game was broken and to move on. It just killed all the fun. And while it may have been fun for the nurgle psyker's player, it wouldn't have been for the rest of us."
So that may paint it a little doom and gloom of a scenario, but you get the point.
With the right group of dedicated people, you could most likely have a super fun and indepth campaign. But these people needed to be dedicated to living out the lore IMO. If they aren't I recommend something else.
Rouge Trader Apocalypse perhaps?