Recording artist Ashanti entertained in the lounge, while Detroit singers Anita Baker and Kid Rock mingled with the enthusiastic crowd.
"There's nothing in Chicago," said John Conyers, a Detroit Democrat in the U.S. House of Representatives. "There's nothing in the Middle West that presents this kind of beauty and grandeur. ... It's reaching out beyond the gaming activity."
In addition to an enormous gambling floor, the casino complex also features a 400-room luxury hotel, spa, restaurants created by Wolfgang Puck and Michael Mina, and a mini-convention center, with a 14,000-square-foot ballroom and 16,000-feet of other meeting space, the Detroit Free Press said.
About 3,000 people -- about half of whom are Detroit residents -- will be employed at the new facility.
Detroit Mayor Kwame Kilpatrick said early cost estimates for the complex were in the $425 million to $475 million range.
"We've invested far more money than we had anticipated," MGM Mirage President Jim Murren said. "The budget kept growing until we got it right. ... This truly is a world-class entertainment destination."