At first you go in and it’s like Space marines? Fancy armor, with fancy helmets, sometimes aquila designs and wreaths and such, perhaps roman-like helmets, capes on occasion, skulls on different parts, etc.
But then you go down one corridor, and suddenly you’ve been down every corridor: pipes, grates, pipes, grates, pipes, grates.
So the emperor had some really fancy pants ideas for armor but he couldn’t spare a moment to think of the decor?
You go into one European palace and you see golden walls, curtains draped everywhere, chandeliers, beautiful artwork, fancy tables and chairs; but in 40k it’s like they had the decor of every human infested planet or ship designed by the ninja turtles.
Every 40k game makes the levels look like the ones from Necromunda hired gun, except instead of brown they go with grey. They look hideous.
Rogue Trader does a good job of visiting lots of different 40k environments, from the ostentatiousness of your palace, to the decrepit ornamentation of Footfall, to brutalist imperial outposts and the pipe ridden bowels of the ship. I get what OP means though, a lot of games just restrict themselves to the dingiest parts of the imperium.