I've been running a Dark Heresy game ... (FINALLY ... I've wanted to for a few years but just never had the right group). I have some concerns about the system for example that combats look like they could be a bit wonky and that the rules looka bit too big and GURPs/RIFTS/Shadowrun-ish for my taste. But all in all at least as far as the character creation night the system is performing great (lol which doesn't mean much really).
I have six more sessions planned in my story arch and then its either on to chapter two or we might move into the Rogue Trader system. I try not to plan massive 50 week long campaigns ... over the years I've seen game after game aspire to do that only to go kaput after about 8 or so sessions. I feel that for pretty much any game planning for between 8 and 12 sessions is best. If you aspire to do more ... fine ... best of luck to you ... but I'd advise to at least do things in 8 to 12 session "chapters." That is how I will run any standard RPG system.
Anyway Just thought I'd comment about how much fun the system is so far
The group is comprised of a Sister of Battle (power armor clad nuns with guns), a Guardsman (who is actually an Imperial Naval pilot ... we sort of hodge podged together something for him out of the guardsman class and its working well so far), an Imperial Psyker, an Arbite (40K cop basically) and a Tech Priest. The group is really balanced and if nothing else we all should get a pretty comprehensive look at the rules.
I am hoping to get really good idea of what the system can do and can't after this run. I'm planning to accelerate leveling a bit and move the group up to around rank 5 or 6 by the time we are done. I'm not a fan of just saying "ok start out at rank/level 5" with a game generally. I find that whenever I've done that as a player or GM people just don't have the buy in they normally do and the game just isn't as much fun. Yet languishing at low level ... yet again ... for yet another game didn't seem that much fun either. So we'll see how this all works out ... so far at least I'm having a blast :)