You won't be disappointed with the single player campaign. It's massive, full of cinematics, in game cutscenes, and achievements to be earned. I'm currently at a point where I'm playing through some missions as Protoss, presumably to briefly introduce players to all of their units and buildings. I'm betting there will be series of missions where you also play as Zerg at some point. All in all, it's a LOT more involved than the campaigns from the first game and I can totally see why they've opted to split it up into 3 parts.
Unfortunately, I'm also falling victim to the random BSOD restart that seems to be plauging a lot of other people on the Starcraft II forums. Hoping that gets fixed sooner rather than later.