This comedy about a low-rated morning television show revitalized by a young producer and a grouchy old news anchor is the finest kind of undemanding Hollywood serotonin-releaser. It’s got a straightforward story and a sharp script that gives headliners Rachel McAdams, Harrison Ford and Diane Keaton plenty of chance to radiate star wattage. Ford is a growling joy as a serious journalist busted down to infotainment TV and Keaton is bitchily brilliant as his shameless co-anchor, while McAdams, with her accessible gorgeousness and naturalistic flair for both verbal and physical comedy, delivers the kind of lead performance that Katherine Heigl keeps aiming for and missing. The movie’s weaknesses---it’s pop-soundtracked almost to death and its rushed conclusion is cluttered with contrived emotional epiphanies---are overwhelmed by its blockbuster-strength charm. –Matt Semansky