system
Given the following post, respond as if you're commenting on Reddit:
human
Why should I read the 40K? What is it about? [40K]

I've been hungry for more Sci Fi after finishing the Thrawn trilogy. 

Edit: Thanks for all the responses, I guess I'm into 40K now.
gpt
40k is Grim dark. If you're looking for a happy ending, look else where. A battle may end nicely for someone but the galaxy will never be free of war and no one will ever win. In spite of that they keep fighting and we keep rooting for them.

Multiple races have a claim to rule the Galaxy and others are quintessential species and forces that want to kill everything and ruin the fun for everyone.

Eldar: the crumbling remains of a once great empire that ruled the Galaxy. Their lust and hedonism birthed the chaos god Slannesh into existence and they've been running ever since so that she doesn't eat their souls.

Orks: Innumerable fungus men that love nothing more than to fight and kill. The breed by being killed and are near impossible to exterminate from a planet, let alone the galaxy. Plus, what they believe becomes true to some extent. Want to go faster, just paint your truck red because red goes faster, duh. Or paint yourself purple and become invisible because "who's ever seen a purple ork?"

Tau: The new up and comers who are making extraordinary technological leaps in a galaxy that is otherwise stagnant in tech. They have one goal, The greater good! Join us to achieve it or prepare to die!

Necrons: sold their souls in order to win a war millions of years ago and now are husks of their former selves. They are automatons that slept for millennia and now that they are waking up, they thirst to kill every last living organism. Even down to microbes.

Tyranids: Xenos arriving from another galaxy. They are basically bugs attracted to psychic activating like a porch light. They eat absolutely everything; stripping a planet completely of all biomass and leaving an unlivable rock. They are heading straight for the astronimcan on Holy Terra.
 
Imperium of Man: Billions of planets, each with billions of humans across the galaxy are lead by the greatest psyker to ever exist, The Emperor, and are in constant battle to exterminate the galaxy of all filthy Xenos and place humanity in their rightful place as rulers of the Milky Way.

Astartes: The greatest warriors at The Emperors disposal. Super engineered human warriors that can fight for days on end, have multiple organs, can sustain multiple injuries and barely flinch or hold back, live for upwards of ten thousand years and much more. They lead The Emperors Great Crusade across the stars.

Chaos: the basic force created parrall to our universe by all sentient creatures emotions. Deep within its bowels reside the four Chaos Gods. Knorne The Blood God thirsts for blood and murder. Nurgle the Plague Lord is the god of death, disease and plague. Slaanesh the Prince of Pleasure feeds off of all desire, pleasure, sensation and lust. Tzeentch the Changer of Ways is the god of Hope, fate, change and Sorcery and weaves the fates of the universe for his own pleasures. At their disposal to reek havoc on the matterial universe are Chaos Daemons and Chaos Space Marines (Astartes who have fallen to Chaos to obey and adore one or all of the Chaos gods).