New York Daily News television critic David Bianculli said the silhouette "looked embarrassingly rude, crude and unfortunately misplaced," Eonline.com said.
He and others noted the positioning of the Purple One's specially designed guitar as he played "Purple Rain" enclosed in screens.
A spokesman for the NFL, which produced the halftime show, made light of the shadowy controversy.
"We respect other opinions, but it takes quite a leap of the imagination to make a controversy of his performance," Greg Aiello said. "It's a guitar."
In the 2004 Super Bowl, the NFL was roundly criticized for a "wardrobe malfunction," when Janet Jackson's breast was exposed while she performed with Justin Timberlake.