Are there any planets or places you've ever wanted to set part of an adventure in? A location so evocative, so interesting, that it becomes real to you as a player/GM?
Lately I've acquired a taste for Hive Volg. I imagine it to be a darker, more vicious version of Petropolis from Ravenor, and will be keeping some of the nicer parts of that particular planet. I can't wait to see how my PC's take it when they meet NPCs who'd rather blow their own brains out than be captured, or where accidental "collateral damage" in a crowded marketplace causes everyone to draw guns or knives and fire at both acolyte and sinner alike. Where people- my pc's included- will have to do things that make them question their faith in the emperor just to get one up on the bad guys, and where no one's a friend.
It sounds beautiful.