The story behind XCOM: Enemy Unknown

For more than four years, a team of 40 or so people in Sparks secretly worked for this Tuesday.

In perhaps the biggest day in Firaxis Games' history, the design studio releases "XCOM: Enemy Unknown," a richly detailed and immersive video game that already has gotten rave reviews.

Firaxis and its parent company, 2K Games of Novato, Calif., need all the buzz they can get. Firaxis wouldn't say how much it spent developing the game, but large releases typically cost tens of millions of dollars. It's a calculated gamble that's commonplace in the video game industry, where companies pursue big-budget blockbuster hits in much the same way Hollywood bets on movies.

"You're talking about a big investment to reach a lot of people with a high end production product," said Steve Martin, Firaxis' president. "It's the biggest game Firaxis has ever produced. … It is a Herculean effort to make something this big."