I've been going through the single player. My one complaint is that they only have a Terran campaign, with the idea that they will release a Protoss and Zerg campaign in expansions, or DLC. I don't mind paying extra, but I like to learn the tech trees through SP. That's going to make getting up to speed in the other races more difficult.
That said, though, the SP is really well done. I'm having a lot of fun with it.