so on the Helsreach note me and my brother love it the second we get that notification of a new episode we stop what were doing and watch it during part 9 i believe we literally pulled over in a gas station so we can sit there and watch amazing work man cant wait for the rest of the book and the film!
If you were to make another series (which would be AWESOME) then maybe Horus Heresy is too long - unless that's what you want to commit to. A 40k short would be great, like "Trials of Azrael", "The Alien Hunters", "The Black Pilgrims" etc.