My group has been playing Dark Heresy off and on for over a year and it is one of our favorite games. We keep coming back because we really enjoy intrigue based campaigns. We love the hard and fast combat system, which can be really brutal at times.
Psykers are a ton of fun, so long as you enjoy being a tad insane.
One of the posts above said that it required a bit of fanatacism, which is true, but it is fun to not tell your inquisitor a few of your exploits, or heretical contacts.