One of my top-ten New York theatre experiences, for sure. Back in that day there many, many posts here about the show (back when there were many, many posts!), with opinions ranging just about as wide as could be ("hated it," "my favorite musical of all time"). It was provocative.
Little bits of trivia:
Sondheim attended and it was reported in NY Post Page 6: "Sighting: NORMALLY staid 'Sweeney Todd' composer Stephen Sondheim, jumping from his seat and shouting 'Bravo!' at the end of 'Adding Machine,' the dark new musical at the Minetta Lane Theatre."
(And I think it was the first show to reportedly have the "you leave the theater, you can't come back in" policy, to one poster's dismay.)