In the great Greek revival, two years ago, one thing went missing – the chorus. In modernising ancient tragedies, from Medea to Oresteia, writers and directors tended to whittle them down into taut human dramas about families in turmoil. Choruses got cut or scaled back. A few remained in full, but to little effect. The National Theatre's Antigone had a smattering of suits, civil servants in stasis, while zombie-like waifs juddered through its Medea. Here, then, is choral power unleashed.