It is an amazingly balanced game. By far, the campaign mode is my favorite. While the story has been a little ... predictable, it is still quite enjoyable. The cinematics that accompany it are almost worth this admittance fee alone. But what draws me is the game. The campaigns have done a fantastic job of walking the line of challenging but not frustrating. I especially like the rpg-like additions that Starcraft II has made in modifying the armies at my control.
While multiplayer crosses over more into the frustrating category, truly balanced games (like a few that I played today) have a great deal of back-and-forth, with victory being both in doubt and just within reach. It amazes me that a game that uses so many units with such different abilities can maintain such a balance. Normally, one group's minor advantage would be enough to tip the scales.
The newest edition is supposed to focus on the Protoss, by far my favorite of the three races to play. I am eager to see what units they are going to add, but I am actually more excited to see how the campaign's progression is going to operate. I hope that it is closer to Wings of Liberty than Heart of the Swarm, although I truly hope that it is something altogether different and better.
They don't have a release date. I'm hoping the game will be available by this spring (if not sooner). Even thinking about it makes me want to play through the other two campaigns again.