Here is a sampling of what they had to say:
Benedict Nightingale of The London Times: "In some ways Harrower's treatment of what's now a well-trodden subject is predictable…There's a destructive symbiosis at work here: one that doesn't only lead to a graphic, gripping description of the principals' elopement and parting but a strange and terrible ending, not unlike the denouement of Sam Shepard's incest play Fool for Love. Both principals are stuck in a time-warp where damage, guilt and passion co-exist. But if the play sets you thinking, it's because of performances packed with feeling: May, sexually alert and teasing behind the rancorous fury; Allam, hurt, indignant yet crumpled, bowed, as if transforming himself into a tortoise complete with shell. They're both terrific."
Nicholas de Jongh of The Evening Standard: "[Peter] Stein's West End revival strikes me with the force of a nagging toothache. It achieves this effect, thanks to the illicit pair's halting, confessional arias and Jodhi May's poignant performance as Una, the girl who falls for Roger Allam's northern loser Ray and erupts into his life 16 years later. She comes for answers not vengeance. Blackbird resembles an Ibsenite inquiry into the past, though lacking Ibsen's flair for psychological insight, creation of characters and nice sociological detail… Roger Allam's drooping, stooping Ray, my view often obscured by a misplaced litter bin, beautifully captures the man's nagging unease and shame. But Stein's production, with strenuous music, sound and lighting sequences, sometimes tilts melodrama-wards."
Charles Spencer of The Telegraph: "This is an extraordinary, no-holds-barred drama that both chills and thrills. It tackles the provocative theme of paedophilia, but refuses to draw glib, reassuring or predictable conclusions. In a magnificently tense and atmospheric production by the great German director Peter Stein, Roger Allam and Jodhi May act out of their skins, giving performances that look as though they have been dragged from their guts. The pair creates a raw, wounded intensity on stage that is at times almost too painful to watch."