I really like any bits of space marine lore I've come across. Theres something about the mix of cool, grimdark, and, extremely silly, combined with the art style.
I'm all about orks. Nothing puts a smile on the face of a guy who takes this game too seriously more than just sidling up to him, saying you're coming at him with a handful of grots, and then watching the dice roll in your favor. They seem to actually like the scenario.