The hit RTS game everyone loves to date...
The species are set into different episodes, 1, 2, and 3. The first episode is the Terran, it is probaly best if you play these in order(thought you don't have to) because then you will understand the story better and understand the gameplay better. Each side has their advantages and disadvantages, their heroes and their zeroes. Simply placing units in the correct position can alow you to win. If you have the expansion pack you can get some pretty cool other units along with a continuation to the storyline.
In addition there is a multiplayer mode and a campaign editor mode. In the campaign editor, you make maps, or edit them, and make campaigns. Simple. In the multiplayer mode you can play the campaigns you made or face off against computers or friends in a one on one melee matches. In the melee matches each team starts off with 300 minerals and 0 gas. You mine for minerals, get gas, make units, make buildings for your base, and conquer your enemy. Each unit has a set attack and defense that can be upgraded in their species proper building. When your army is large enough, a 200 unit max, you should attack the opponent's base, you probaly don't want to wait to long or they'll conquer you.
All of these things are what have made StarCraft such a successful series. This is a definate buy.