You're right GW, if there's going to be two "races" and six factions each and their only real difference is in appearance and the like would make the not really worth playing (A thing we know Stardock would never do). Of course they would make the six Fallen factions radically different, examples...
WARNING another set of analogies are coming;
One could be like X-mens' Wolverine: tough, direct, and insanely intelligent who are just trying to overcome their past in hopes of a brighter future. While their polar opposite could be akin to Sabertooth or Kratos in that they totally imbrace their darker tendencies and just want to watch the world burn. Another could have Magneto's philosophy in that in order for them to survive they would need to remove those who wish them dead. While another could have a Darth Vader complex, doing morally questionable things for the greater good. Of course, you gotta have one like Edmund Dantes in The Count of Monte Cristo for they have been victimized, whether it really happened or not, and have been stewing over it long enough not only to desire to destroy their enemies but everything they hold dear.
That's all I got.
Oh, sorry about misinterpreting what you meant about the Fallen being simple, Landisaurus. I agree they should simple in the way of being practical not simple like the ogres in the Gummi Bears cartoons. While they would provide a lot of comic relief, I for one would get little peeved if every one of my commands was cheerfully answered with, "Okay, Dukey"