File1317990517.jpg-(90 KB, 495x700, 12342146576.jpg)
Just thought I'd drop in with a couple ideas:
Make sure that the relations/diplomacy system is as varied and intricate as you can make it without it being asinine. Different chapters, Imperial organizations, leaders within those organizations, planetary populations, etc should have different temperaments. For example: say that you and another chapter destroy a group of xenos. The other chapter pulled most of the weight, so basic fairness would dictate that they receive a relic that was recovered. However, you have actual, physical control over the relic and refuse to turn it over. Obviously, anyone would be pissed about that, but not all chapters would react the same way. Black Templars might refuse to be involved with you in anything ever again, but the Salamanders might forgive you over time.
I don't expect battles to be detailed and hands-on like in DoW, but they should still be much more complicated than simple math equations where you take the rank and variety of your soldiers, plus the quality of their gear, their morale, etc and compare to your enemies' and whoever has the biggest number wins. You should be able to maneuver your troops throughout the battle - order certain troops to charge, fall back and perform some other tasks, retreat and then re-engage the foe at one of their flanks, pretty much any general maneuver you can think of. And instead of battles being just some blip on the map, they should be more like a temporary part of the terrain, and carry on over time like any normal event would instead of freezing time and space like battles do in other games, like say, Total War. For example: say your ships have engaged an Ork fleet, you're duking it out. Then some dumbass merchant tries to fly their ship through the middle of the battle. There should be a good chance that they'll be blown to pieces. And as the battle progresses, other forces should be able to join in.