One they are more open to women which is a mark over Deathwatch.  Yes, there are Sisters of Battle but Sisters can't participate in the Cohesion rule system which is a cornerstone of Deathwatch play.  Granted playing a male Space Marine isn't really like playing a "guy" character but it does deter women from playing.  Only War is a possibilty but while having access to the book I haven't gotten a chance to read through the pages.  My brother decided to run an Only War game at his work so I don't get to see the book and I'm not spending 60 whatever dollars on it.<br/><br/>Dark Heresy is cool but seems pretty strict.  I love all the conspiracy theories and stuff but it does lack that bravado.  Rogue Trader has bravado in spades.  Rogue Trader also has a lot of kinky stuff possible in the mix such as slave trades, access to brothels, exotic alien races, etc.  There's also the swashbuckling lifestyle.  Black Crusade is pretty much all about the naughty naughty and baddies of the universe.