Total Waaaagh: Orkses Is Da Tuffest
EDIT:
But srsly, I'd love a Total War: Horus Heresy ... on the scale of the old Epic 40K games, with Titan Legions and entire bloody chapters of Spehss Muhreens.
The turn based movement on a campaign map of the segmentum solar etc .... but they'd not be allowed by Games Workshop to do it on too big a scale because it'd rape the fluff (damn that sounds nasty ...), the only thing more stagnant than the Imperium of Man is the plot progression from GW - but then again, it is a Dark Age after all.