Can you think of any shows that had very negative buzz or audience reviews during previews, and then turned around to become critical and/or popular successes?
Much of the audience was noticeably restless and bored at the opening night of SUNDAY IN THE PARK WITH GEORGE. I know this because people were talking aloud during the second act about how bored they were. During the laser show, the lady next to me shouted, "Maybe this would be fun if I were stoned!"
The next morning, Frank Rich's rave review made the show a success d'estime.
(ETA the same could be said of several of Sondheim's shows. I love PASSION, but most people I know are openly hostile to it. Yet there's that Tony Award for Best Musical.)
A Funny Thing Happened on the Way to the Forum is often held up as a classic example of a show that was struggling out of town/pre-Broadway until they nailed the opening with "Comedy Tonight" and turned the fortune of the show around.
For a more modern example, A Gentleman's Guide to Love and Murder only did so-so business for the first several months of its run. They held out and business picked up with the announcement of the Tony nominations, and then obviously a huge surge in business for the remainder of the year after winning Best Musical.
IIRC, PIPPIN got so-so reviews from many critics and was saved by a very catchy TV commercial. It is usually mentioned as a turning point in the power of TV ads v. critics.