Astonishingly bad. This Special was so clumsy a script from a writer who should really know better (if one goes only by his extensive experience). RTD's rare creative moments, such as his gunshy Britain or the occasional oneliner that doesn't fall so flat it's as two-dimensional as his plotting, are dwarfed horribly by the lazy premise. The episode, from about the meteor impacts on, was so horribly unoriginal that entire catchphrases, such as the chant "kill, kill, kill" that the robots utter can be discovered wholesale in The Robots of Death, from which the story inherits almost all of its setup. Same goes for the robot's arm caught in the bridge door, an image similarly lifted. The rest is borrowed from Enlightenment, another original series episode, leaving almost nothing but the fecal deposition of awkward "character moments" that so completely characterizes RTD's style.
That Davies is one of the most successful writers in Great Britain is proof that life is ironic at its core.