Terrans are, in my opinion, the best race in the game. All of their units are pretty versatile, since the main land unit (the Marine) and the main air unit (Wraith) can attack both air and ground targets, making either one capable of holding off an attack. Most of the Terran Buildings can fly, which can help if you get caught by an early Zergling rush; just lift your CC, and you are saved. Also, after an attack, you can repair units that are almost dead, saving you lots of resources, as well as time, in the long run.
The Protoss are the most technologically advanced race in StarCraft. Many of their units, like Probes, Shuttles, and Reavers, are robots, while other units, like Dragoons, are robotically-enhanced. The Protoss are also very powerful when it comes to psi-oriented spells. Both the High Templar and Dark Archon cast several spells, all of which can, if use in the right circumstances, do much damage to enemy units.
I think that the Zerg look way cooler than the other races in StarCraft. The Zerg have a centralized center of unit production; no matter the unit, it is going to be built/grown from a Hatchery/Lair/Hive. This means, build multiple hatcheries as soon as possible, so that you can have plenty of larva ready to mutate. Also, since the Zerg 'grow' their troops, and for the most part they are cheap, they depend on mass numbers of them (especially in the case of zerglings) to win battles; don't expect to make a few zerglings and win.
