40K universe. You know why? Because there are no good guys or bad guys. The entire universe is a race to the bottom, a race to see who will be able to survive and who cannot. The "good" guys (a.k.a the guys who we are supposed to root for) is run by a genocidal, facist, inefficient, all-powerful government which thinks nothing of killing billions of civilians to prevent even a single loss to its overall influence
The "bad guys" are the ones who are fighting for the freedom to live and fight the way they want to or were cast out by society and are persecuted for something they can't even control.
No matter the sacrifices, no matter the pain caused, and victories attained, peace is unattainable. Every sacrifice is in vain and every single soldier is merely a cog in a bureaucracy that is so slow that entire planets can go missing in the paperwork.
This is a universe where blatant racism, witch hunts, the torture of billions, and the systemic rape of entire systems of people was the ultimate saving grace of mankind. Without the deaths of billons of people for being "different" mankind would have been destroyed.
The universe uses many tropes and cliches, but combined with its unique setting, there is nothing quite like it out there. No other universe really gets across that the galaxy is a huge place filled with conflict. No soldier, no matter how powerful or influential, can change the outcome of a war. How does a single person stop an invasion that is happening simultaneously across the entire galaxy? How does a single person, no matter how strong, stand up to a orbital bombardment? The fact that the universe acknowledges that nothing anyone can ever do can stop the entire galaxy from continuing its everlasting war is what is so interesting to me. Its a deconstruction of the clean and happy sci fi that is prevalent.