Today, the biggest retail launch in entertainment history is expected to bring in an estimated $80 million, gaming industry experts say. It's not the latest from the folks at Disney, not a Jay-Z album, not a special DVD collector's edition of "The Godfather."

It's a video game.

Halo 2 -- the sequel to the sci-fi man-vs.-alien juggernaut, which involves a battle over the secrets of a ring-like planet known as Halo -- is creating the kind of buzz usually reserved for a Hollywood opening of, say, "The Incredibles." That animated film grossed $70.7 million over the weekend. In contrast, Halo 2 -- with preorder sales of 1.5 million copies of a game that retails for about $50 -- guarantees a one-day take of at least $75 million. It started leaving store shelves at 12:01 a.m. today, with staff at outlets such as GameCrazy and EB Games preparing for lines reminiscent of a Harry Potter book release.

For three years, the excitement over the sequel has been fueled by the original, released in 2001. Many fans of Halo bought their Xboxes simply to play the game.

It was all Halo for 13 hours Saturday at Pat Dwyer's three-story, four-bedroom home in Jeffersonton, near Warrenton, Va. His three kids were sent away. His wife was gone for the day.

Dwyer, 36, had invited his friends the Mourad brothers -- Ramsey, 35, and Reem, 34, owners of their own telecommunications company -- to come over, their Xboxes in tow. Together, the men own four Xboxes, which they set up with four TV screens. They were also stocked with two cases of beer, lamb steaks, a seven-layer dip, peanuts and cigars. The Virginia Tech-North Carolina football game could be heard in the background -- blasting from an Internet broadcast in the family room. These thirty-something guys -- "the Atari generation," says Dwyer, referring to the classic platform, "with the orange buttons and the stick" -- are not far from the typical video game player, who is 29 years old and male.

The fact is, as the industry has matured, so has its players. U.S. game sales last year were $7 billion, and this year's figures -- with such hits as Halo 2, Grand Theft Auto: San Andreas and the yet-to-be-released Half-Life 2 -- are expected to top that, industry watchers such as NPD Group say. In a way, Halo 2 is symbolic of the new wave of entertainment, which depends heavily on virtual reality. The next versions of Sony's PlayStation2 and Microsoft's Xbox are due out in the next two years and promise even more enhanced visual effects and realism. This is interactive entertainment: You're in the game. In Halo, if you're shooting, the controller vibrates. If you fire rounds into a wall on the screen, the bullet holes stay there.

To Dwyer and the Mourads, playing Halo together, which they do every four or so months, is a way of socializing, a way of hanging with the guys. ("Some women were invited, but they were busy," Ramsey Mourad says with a shrug.) They could be outside at a park, shooting hoops. Instead, they're in the family room -- with Redlo, the pet snake, in a cage in one corner of the room, a pink doll house in another -- covering the windows with blankets secured with duct tape. Too much glare on the television.

Reem Mourad talks about Halo as if it were a movie or a book or a song.

"I realize it's only a game," he says, a glass of beer in hand. He and the others are taking a five-minute break. "I haven't lost sight of reality. But there's a story within the game, and that's what attracts me."

The original Halo is a single-player game, with stunning, colorful, cinematic visuals. The main character is Master Chief, clad in armor and a visored helmet, a human super-soldier whose goal is to discover the secrets of Halo and save it from the Covenant, the enemy aliens. It has a story arc. It has evocative, monk-like music. It has fast, violent action.

Joe Staten, the 32-year-old soft-spoken leader of Bungie Studios -- a coterie of 60 or so coders who work out of Redmond, Wash. -- is the game's writer and director. Bungie was a small game developer with little success, he says, before the first Halo was shipped out in 2001.

With a budget of more than $20 million and a soundtrack that includes original music from bands such as Incubus, Breaking Benjamin and Hoobastank, Halo 2 is a production on the order of a Hollywood blockbuster. The sequel brings the man-vs.-alien battle to Earth, where Master Chief and the raiding Covenants duke it out. The game is now multi-player, with 16 participants fighting simultaneously. Online, on Xbox Live, gamers can join with or fight against others from around the world.

Microsoft's Xbox, which released Halo 2 exclusively, is still a distant second to Sony's PlayStation 2 in terms of market share. But the first Halo sold more than 5 million copies worldwide, and it's a bright light for Xbox. So, inevitably, the marketing campaign for Halo 2 has been intense, with billboards, commercials, even movie trailers. This week it will be released in 27 countries and eight languages. Prima, a division of the publishing giant Random House, has an initial print run of 1.1 million strategy guides, at about $17 each, for the game -- one of the largest print runs this fall from any Random House division, second only to the paperback of John Grisham's "The Last Juror."

The Toys R Us in Times Square is the epicenter of today's launch. More than 6,500 retailers, including more than 30 stores within 15 miles of the District, planned to stay open last night for this morning's launch. The phones at GameCrazy, on Jefferson Davis Highway in Alexandria, rang constantly yesterday, as did the ones at EB Games in Prince George's Plaza in Hyattsville, with most of the callers asking about Halo 2.

"Some people who haven't preordered it are calling, too," says Kurt Eddy, 27, at the Alexandria GameCrazy. About 150 people preordered, he says, but adds that the store will have more copies on hand.

"Call a spade a spade: This means that the video game industry can no longer be ignored," says David Riley, senior manager for NPD Group, a New York-based independent market researcher. "There's been great word-of-mouth about this game."

The first Halo, Riley points out, has been in the annual top 10 of video game sales since 2001.

"Halo 2 has the 'wow' factor, the heat, the Q factor, I don't know what other jargons we use in Hollywood," adds Chris Marlowe, a new-media reporter -- "I cover whatever's next," she says -- for the Hollywood Reporter, a Los Angeles-based trade publication. "The game, in a way, has become a cultural flashpoint. It's crossing demographics. It's crossing cultural lines. Everyone is aware that this game is coming out."

The Mourad brothers are getting their copies Thursday.

Dwyer is getting his on Thursday, too, from a friend who owns a video game store, Replay, in Stafford. The corporate sales executive, often busy with work, says he isn't an addict.

He only plays with friends -- and, since the game, rated M for "mature" is violent, he only plays when his children, ages 4, 7, and 8, are not in the room.

On Saturday, as he sat in front of his 32-inch television, both feet up on a chair, the soundtrack of the original Halo playing in surround sound, his mind was on Master Chief.

The kids, by the way, are with Grandma Sue -- Dwyer's mom in Reston -- who took them to see "The Incredibles."

A scene from Halo 2 for Xbox, which was released at 12:01 a.m. today with preorder sales of 1.5 million copies at about $50 each.Pat Dwyer, left, and Ramsey Mourad play the original Halo on two TV sets during a 13-hour marathon Saturday at Dwyer's home in Jeffersonton, Va.