Last night, I noticed there’s an Xbox achievement in “Grand Theft Auto IV” called “Liberty City Minute.” It awards the player 30 points for completing all 80-or-so of the game’s main-story missions in 30 hours or less.

That sucks. Why?

The signature feature of “Grand Theft Auto” is its free-roaming, open-ended gameplay. The series revolutionized the industry by introducing the concept of “sandbox"-style gameplay, giving players a sprawling urban environment to explore and interact with however they see fit. Gamers can go shopping, watch TV, listen to the radio, go on dates, shoot pool, play darts, go bowling or just drive around—and the sense of liberation from the usual confines of video game “levels” can be exhilarating.

The “Liberty City Minute” achievement throws all that out the window and encourages gamers to play “GTA IV” as if it were a linear shooter, tackling one mission immediately after the next, with nothing in between. In other words, it robs the game—and the player—of everything that makes “GTA” such a unique and engrossing experience.

Through my first 30 hours with the game, I’d only completed about half the game’s missions. Friends who unlocked the “Liberty City Minute” achievement say it took them between 27 and 30 hours without doing anything else between missions. No dates with Michelle, Kiki or Kate; no stealing exotic imports for Brucie; no delivering contraband for Little Jacob. Nothing. They tell me they rarely even drove anywhere—they always hailed a cab and skipped the ride.

Personally, that doesn’t really sound all that fun to me. But more to the point, it doesn’t sound a thing like “GTA.”