The Warhammer 40K DLC for PowerWash Simulator is easily the worst of the paid DLC so far. I can't really recommend it. It's probably neat if you're into Warhammer, but I am not.
I mostly found it tedious. Everything you clean has a ton of intricate little parts and it just gets tiresome. The final object to clean is huge. It was clearly designed with co-op play in mind. Probably a blast with friends. Solo, it just got tiring by the end.
My other complaint is that all your cleaning takes place in a big warehouse. There are lit candles everywhere. Does spraying the candles with water do anything, like turn off the flame? No. The water doesn't interact with the candles at all. It's such a weird choice to have candles in a game about spraying stuff with water, just to have them be static objects you can't really interact with.