I just saw it yesterday, in fact.
Maybe it was bad case of high expectations, but I didn't love it. I could watch Meryl Streep for hours and thought her performance was great. I thought Kevin Kline's performance was dear and kind of an Otto (A Fish Called Wanda) redux, which cannot be a bad thing. But I couldn't figure out the tone -- the slapstick wasn't funny enough; the ominous wasn't particularly ominous; the sad didn't reach me. It was, in a way, as through the glass in the booth -- just didn't reach me.
I was annoyed by the audience, who seemed to confuse what was familiar with what was funny, and therefore laughed at everything.
I was also looking for a gimmick that didn't really happen -- I wanted the show to be in stricter real-time. It almost was (it's a two-hour show), but there was no News from Lake Wobegon, and the reading of the letters was aborted, and not all that amusingly, and the sound-effects thing could have been really satisfying but wasn't.
But hooray for Robin and Linda Williams -- they rocked.