Yes, there is an official "Watchmen" videogame coming out called "Watchmen: The End Is Nigh" but this ain't it.  The UK site for the film has a great little feature called "Minuteman Arcade".  Made by Viedt Industries (awesome), the game has you playing as either the original Nite Owl or the original Silk Spectre as you fight crime, beat-em-up style.  It's relatively easy and repetitive (as are most beat-em-ups) but the charm of it is undeniable.