They got ded big shooty guns dat'll kill tons of boyz, but if yer can get near em den you've got a chance. Just gotta make sure you bring loads of boyz, coz you ain't gonna have a whole lot left when you get close enough ta crump em.
Sorry, I can see how my statement could easily be misinterpreted.
I should have said dark heresy is about player characters who are members of the inquisition.
And yeah, I'm sure the rules can be stretched to include aliens, in fact the 3rd game in the line is supposed to be about playing xenos but even so, the universe is not set up to have a group that consists of a space marine, an IG grunt, a commissar, a Tau water caste, and a genestealer cultist all working together and being friendly and treating each other as equals, and in my experience that is the kind of group RPG players will want to put together.
If you've got a group of players that are all willing to accept a whole bunch of restrictions on character creation and work together to make a team instead of a collection of individuals, great. I have yet to find such a group in 25 years of active role-playing. Once Upon a midnight dreary....
One version that might be included in this little chat is inquisitor. A version of that could be modified to tau and warhammer 40k standards. GW SPECIAL The Gue\'vesa followers of Khorne killed my team, my father and burned me when i was a Shas\'la.
Now I am a Shas\'el. I strive to end the followers of Korne. The fire that burned me still burns in the deepest place in my heart. It forever shall burn. I am now known as the Burning knight.