The development of Starcraft's 2 story-line is based on a war between 3 races (Terran, Protoss and Zerg), who fight for freedom and/or domination. The whole game has a lot to offer, not only in the campaign, but also on multiplayer mode.
The campaign has more than 20 levels, in which you have to complete challenging objectives while enjoying the great looking cinematics and dramatic story-line. You don't have to play the first starcraft game to understand this materpiece, since everything is explained through it.
The main race you will use in the campaign are the Terrans, but expect some quests from other races as well. The voice actors also did a great job and the music is good and fits the game.
As for the multiplayer, at first you might get really frustrated, but with a little practice you will be addicted to it. I have two friends who began playing 3 months before the expansion "Heart Of The Swarm" came out, they got beaten up at least in each 4 of 5 games. But as they learned how to make units faster, and how to exploit all the race's weakneses they got better, to the point they now are diamond (which is a high rank).
If you like strategy games and have a decent pc, this game is a must have.