Halo Wars took the Halo universe & dumped it into the RTS genre. For me, it was as successful an RTS can be on a console. Needless to say, I was plenty happy to hear that a new expansion pack, called Strategic Options, was in the works.
In addition to new MP maps, we will be getting 2 new gameplay modes. GameTrailers posted a couple of videos that will show you what the new games mode are all about.