>This thread again
First, all the Primarchs die. All of them die gloriously in combat.
Secondly, the original Chaos Legions stay together. For the most part, legions like the Night Lords, World Eaters, and Alpha Legion break up far more than the Iron Warriors, Death Guard, or Thousand Sons.
Third, don't explain shit. Here's the world, lots of mystery. Where did the Carcarodons come from? Who knows! The worst thing you can do to a world is to fill in the cracks too much.
Fourth, tone down the Space Marine wank by at least like 50%. Imperial Guard are the real heroes of the Imperium.
Fifth, bring Sisters more to the front. They're wonderful characters that really get to the heart of what 40k is. Replace most stories that follow Space Marines with Sisters of Battle and Imperial Guard. Space Marines should only be seen when the sky is falling, all is lost, and through heavy smoke or something else that makes them hard to see.
Sixth, make the Imperium slightly less fucktarded. Non-aggression pact with Tau and Craftworld Eldar.
Seventh, like the Imperial forces, shift more focus of Chaos forces to mortal servants. Chaos Space Marines and Daemons should only appear when things get really heavy.
Eighth, the original Ollanius Pious story is canon then set in stone.
Ninth, show more examples of worship of each of the Chaos Gods. Develop the philosophy behind each more.
Tenth, ALL HAIL THE PRINCE OF CHAOS!