Iron Man 2 blew up box offices this weekend with the fifth biggest opening in history. Its $133.6 million haul in the U.S. and Canada kicked off a big summer slate of films and worldwide Robert Downey Jr. and Co. came away with $327.6 million. Revenue will likely keep rising: The blockbuster garnered an “A” grade in the word-of-mouth category. Far away from Iron Man’s nine-digit figure was runner-up A Nightmare on Elm Street with $9.1 million, down 72 percent from its chart-topping debut week.