Monsters vs Aliens is such a barnstorming title that it's a pity that DreamWorks' slick but empty new cartoon does no more than the bare minimum with it. A 50ft woman (voiced by Reese Witherspoon) is recruited by the US government to repel an alien invasion, alongside a few other 1950s B-movie monsters. It has all the overcomplicated, video-game-friendly action sequences we've come to expect from computer animations, as well as all the ironic one-liners and pop-culture references. But it doesn't have much else except the much-vaunted 3D effects, which are diverting at first, but which you get used to after the opening two minutes. A fun time-passer for the Easter holiday, but destined to be forgotten by the time school starts.