The Roundabout has been on a good streak, with daring and punchy revivals of Picnic, Cyrano de Bergerac, The Big Knife, Man and Boy andLook Back in Anger (not to mention several good new plays). Machinaltakes the biggest risks, and has the greatest payoff. If you care about American theater-particularly its experimental heritage-go now. I seriously hope that the Roundabout's audiences are thrilled by what they see. But if Todd Haimes gets complaints from people who were rattled or disturbed, that only means the machine is working smoothly.