Starcraft is the only PC game I ever got really into during my youth. It is a legend in the real-time strategy genre, and a national past-time in South Korea.
This game revolutionized the real-time strategy genre, offering three well-balanced yet distinctly different races, each with their own unique characteristics, special powers, and preferred strategies. The Protoss have the most expensive units, but also the most powerful. The Zerg, conversely, have cheap and weaker units but achieve strength in overwhelming numbers. The Terrans strike a balance between the two (and....have mother effin' Siege Tanks, the best unit ever conceived of in an RTS).
Starcraft immerses the player in its world of near-infinite strategic possibilities. For every strategy or special power, there's an effective counter. Voluminous books and online guides exist, to the point where anyone can find a strategy tailor-made to suit their preferences. And there's a primal satisfaction to blowing the hell out of your enemy's base with Terran Siege Tanks, or watching your swarm of Protoss Carrier Interceptors erase your opponent's defenses...or launching a cheap Zergling rush that wipes out your enemy's gatherers before they can even launch one unit.
But the best thing about Starcraft is this: You can have fun with it, even if you're a mediocre to average player (like myself). I know that there are millions of faster, more effective Starcrat players out there, but this game (and its recent sequel) keep me coming back for more. And speaking of Starcraft 2, I'll have it known that I bought a brand new PC, and upgraded its video card and power supply....just so I could play that game.