For an expantion pack, there is alot for this game to offer.
To tell the truth, I didn't go too deep in the single player to find out what the story is, I do enjoy a good story in my games. But, I went strait to the skirmish to play around with the Imperial Guard. I did the tutorial, (yeah, I know I shouldn't have) but found myself pushing on ahead, by the time the tutorial was showing me the camera controls, I had an army of Guardsmen assembled and rolling. I had captured all the territories on my side of the map already. So I guess I didn't need to do that.
Then, I played around in a regular skirmish. I had a chance to build a few Basilisks, Ogryns, even the Baneblade. But then the match was over. Then, I played another, as the Chaos Space Marines and messed with the Khorne Berserkers. There cool. Then, just to find out, I tried the Single Player. First Disorder,(cause I like being the bad guy) I found it mildly difficult considering you only start out with a squad of orks and a warboss, then it got exciting. I made it to the second level, then quit.
So, I guess if you are a fan of Warhammer 40,000 or a fan of RTS in general, check it out.
ChaosGames