Although I'm not an RTS guy, I absolutely fell in love with this game, and MUST have the expansion. With that said, I too am really disappointed that they didn't decide to include a new race. IG are like new units of the same old human army and, as someone else said, you already got to play them somewhat in the first version (and they weren't too exciting). With Tyranids, Necrons, and Tau obviously missing, I just can't understand why they chose new units of an old race. *shrugs*
But I'll buy it anyways. And if you're really interested, there are mods in development for all of the aforementioned races, some of which are looking like they're shaping up quite nicely. And more human units like Daemonhunters (Grey Knights), Witch Hunters/SoB, Rhino variants, Iron Legion (different slant on IG), and more. There's also a Thousand Suns mod for Chaos that looks like retail quality IIRC. I really should get off my arse and try some of them out.
And best intro movie I've seen in a long time. I hope these guys are returning for the expansion.