I assume it is illegal in most states. In Illinois:

"HB 960Mandates that a vehicle equipped with visual media technology cannot be operated if the technology is on and the screen is visible from the driver's seat. Which means if someone has one of those video screens to play movies in the car, it better not be in the driver's line of sight. "

Not to be overly dramatic, but it would not be good if the EMT's or Policeman pulling you out of a wrecked X5 noticed Batman playing on the display, particularly if someone died.