CHICAGO — From the rocket-propelled grenade that shoots down a police helicopter to the punch in the face delivered to a former friend, the depictions of realistic violence in the newest "Grand Theft Auto" videogame are raising fresh concerns.

And gamers couldn't wait to play.

The release of "Grand Theft Auto IV" was such a big deal that, as with the Harry Potter books, retailers held midnight release parties Monday to mark the title's arrival.

The controversy surrounding the phenomenally successful game series struck early. Facing renewed complaints that the game's violence is inappropriate, the Chicago Transit Authority late last week removed advertisements promoting the release from its buses and trains.

The tussle over "Grand Theft Auto" is partly a debate over its value and partly a discussion about how to keep children away from a title that everyone agrees contains material they should not see.

"People think videogames equal kids, and that if it's just a game, it should be fine," said Robin Burke, a game-development professor at DePaul University. "But the idea that a game is made for a mature audience, we (as a society) don't have our arms around that yet."

Indeed, even though games have clear ratings, like movies, they often are ignored by parents and sometimes by retailers.

A study last year from MediaWise and Harris Interactive found that 72 percent of parents don't understand game ratings. What's more, 37 percent of parents said they rarely used those ratings when buying a game.

Some critics want to ban stores from selling games like "Grand Theft Auto" to minors, though that approach was found unconstitutional. Others wonder what possible redeeming value there is for anyone to play a game in which a joystick is used to simulate murder.

Jeff Smith, a 30-year-old information technology professional, said games like "Grand Theft Auto" are an adult form of entertainment, an elaborate, increasingly sophisticated, action-packed fantasy world.

"As gamers get older, into their 30s and 40s, they want more adult games," he said. "Gaming is a good way to blow off steam. It's almost a type of voyeurism, a peek into the lives you see in film. Mobster movies (like "The Godfather") are big because it's a peek into that world.

"'GTA' is like that, but it takes you an extra step," he said, noting that gamers have "unbelievable" control over what they can do. "In real life, if you had a bad day trying to catch a cab, there's nothing you can do. But when you come home, you can punch a ('GTA') taxi driver in the face and take his fare money."