The original production has never been bettered and it must be difficult for those who didn't see it, or young people who think it is all sticky cutesy sentimentality to understand why the show worked so well. Part of it was the timing.
Never intended as a kiddie show, the original authors wrote it as a response to the cynicism of politics post-Watergate. It had a sophistication to it that was unexpected and appealed to all audiences. It also delivered the pleasures of an old-fashioned musical, but with a polish and slickness that was up to date.
The original cast was indeed lightning in a bottle, but there were also superb replacements over the length of the run.
The physical production, especially David Mitchell's set, were state-of-the-art. The sets just magically danced and glided into place, and I can remember some of those scenic transitions better than from shows I saw last year. (Paging Someone In A Tree?)
I think perhaps the thing that the original production had that has been absent from all other productions is Mike Nichols. Even when the show was working like gangbusters pre-Broadway in Washington, D.C., he pushed them to go further. All told, that original production was one for the ages. A perfect experience.
Begin at the beginning and go on till you come to the end: then stop.