I really enjoy playing Halo Wars. It's fun, strategic and simple to play. Sure, it may be dumbed down from most real time strategies but that's what makes Halo Wars fun in my opinion. It would be awesome if Microsoft gave the green light for a sequel. I'm sure it sold well considering it was a Platinum Hits title.
Or maybe Microsoft can publish a Gears of War themed real time strategy just like Halo Wars. Now this would be bad ass! It can be a prequel and the story can be borrowed from one of the books or something. Or just a brand new story.