Art review Whirligig of horrors reveals painter's genius and humanity

Teeth. We all have them, or start out with them. We're supposed to take care of them, so we can flash a smile. But for Francis Bacon, they are a glimpse of death in a living human face, a white hardness that will persist when all our soft matter is gone. In Study of the Human Head, a man in a dark jacket smiles out with perfect teeth. Then you realise Bacon has superimposed an X-ray image of the human head on to this living man. It is the grin of a skull.

- Jonathan Jones

The National Portrait Gallery has assembled a truly biting show of Bacon's portraits and meditations on portraiture. Not only is it the best Bacon show I have ever seen, it also answers all questions about his greatness. Was he a genius or a showman, a seer or sensationalist? Critics started arguing from the moment he burst out of nowhere in the 1940s to shock a wartime London you'd have thought unshockable. The critic John Berger accused him of "horror with connivance". Fans of fellow artist Lucian Freud still sniff that his friend Bacon was a slapdash, melodramatic artist. And they'd be right - but only if the definition of a great portrait was a recognisable depiction.

This exhibition is a whirligig of horrors without a shred of connivance. It exposes, like a body dissected on a table, both the monstrous modernity and the timeless humanity of Bacon. It begins, after an almost gentle encounter with a late self-portrait, with the disfigured, hollowed, claustrophobic portrayals of seated men completed in the late 1940s and 1950s.