So, here we go again down the nerd hole.
This past year, I have been reading the Warhammer 40 setting books, and I have fallen in love with the Soul Drinkers saga. The books revolve around a legion of space marines that rebel against the iron–fisted human empire. They begin on a quest of rebellion, seeking the light of the gods, only to wind up cursed and in the midst of a war between the cosmic forces of order and chaos.
The books are a mix of science fiction, fantasy, and cosmic horror. The soul drinkers travel across the universe, fighting demons and trying to overthrow the imperium of man. The books are filled with massive battles and a deep 40k mythos.
With the occult and unsettling themes that occur throughout the story, I would recommend that you avoid reading if you are prudish. The books are gothic horror. At the same time, it feels like you in the midst of a halo/space marine power fantasy.
If you are looking for books to start the Warhammers 40k universe with, I can tell you that Soul Drinkers is a good place to start.