When Houser and his brother, Sam, launched the GTA series in 1997, they essentially invented the “sandbox” genre, in which players are let loose in a virtual city to do almost anything they please. In the GTA series, that generally translates into random vehicular mayhem, juxtaposed with assignments that move the protagonist forward in the world of organized crime. In GTA IV, players assume the role of Niko Bellic, a new arrival from an unspecified Slavic nation, who comes to Liberty City to work for his cousin’s car service in a Brighton Beach–like neighborhood.

By the end of this week, Niko should be well on his way to being a household name—analysts say initial sales following the game’s April 29 release for the Xbox 360 and PlayStation 3 could top $400 million worldwide. That’s more than most of this summer’s ostensible blockbuster movies will gross during their entire theatrical runs, and more than twice as much as the biggest movie opening ever. If predictions are accurate, GTA IV will bring in more money in its first week than any cultural artifact ever has in any medium—and this from a game not intended for sale to anyone under 17.

The Roman numeral in the title may confuse casual gamers, as this is the fourth entry in the series in the years since GTA III. The lack of a number doesn’t mean that 2002’s Grand Theft Auto: Vice City (a riff on Scarface and Miami Vice set in the ’80s) or 2004’s Grand Theft Auto: San Andreas (involving early-’90s ghetto gangsters) have suddenly been deemed lesser games. Consider the number to be a thrown-down gauntlet, an indication that the processing power of today’s game consoles (GTA IV is the first installment for the Xbox 360 and PlayStation 3) has allowed Houser and his colleagues at Rockstar to reinvent the series. “There’s nothing as easy to define in three or four words as the leap from 2-D to 3-D [between GTAs 2 and III],” says Houser. “But I think there’s enough there that within ten seconds of looking at it, it’s obvious we’ve moved forward.”

Certainly, GTA IV is the best-looking game in the series, but Houser isn’t just talking about graphics—he’s referring to the ability to “have that many people onscreen, that much AI running, that many varied behaviors” among passersby and drivers, which are key to the game’s atmosphere.

Many fans unfamiliar with New York assumed that the Liberty City featured in GTA III was a faux Manhattan, but Houser—a native Londoner who has lived in New York for a decade now—says, “We weren’t really interested at that point in doing real places. We just wanted to make it feel like America.” The size of the game’s world grew considerably in Vice City (which spoofed Miami) and exploded in San Andreas, which was modeled on enormous swaths of California and Nevada. This time, Houser opted for a much smaller but far more detailed environment, one for which reference material was available right outside his door (although the game’s producers are based in New York, most of the actual programming happens in Scotland).

If there’s one secret to capturing the flavor of New York in a video game, it may come down to the art of the judicious choice. “Aaron Garbut, our main art director, is very good at picking out the essence of a place. “[He’ll look at some photos and say,] ‘These two neighborhoods are broadly similar, so let’s smash them together. We don’t need both; it’s going to feel the same,’” Houser explains. “For someone who’s been here, it’s going to feel like New York; for someone who’s never been here, it’s going to feel like their imagination of it.”

Grand Theft Auto IV (Rockstar Games, $59.99) is now available for Xbox 360 and PlayStation 3.