I am sure that there are people who are seeing the show because they are fans of the Spider-Man franchise and are actually curious about the musical adaptation of it. I am also sure that there are others (like my brother and his girlfriend) who expressed interest in seeing the show only because it has reached car crash like status with regards to how often it has been in the media.
Regardless of the reason, people are eager to see this as proof of its good numbers. Yet, I don't see why the producers would mind if someone were to review the show at this particular time. The numbers are good, and I do doubt that a negative review will change that. I do believe that gone are the days when a critic can kill a show with just one stroke of the pen. I think that this show is proof that there is no such thing as bad publicity and that even the negative news stories that this show is getting is enough to get people to want to buy tickets regardless of if they are Spider-Man fans or not.
Yes, I do agree that critics should follow the unwritten rule that you should wait till opening night to publish a review. However, with a show like Spider-Man, that has delayed opening time and time again, I don't see the difference between a critic choosing to buy a ticket and reviewing it on their own time and the difference between a theatre blogger or message board poster spending their own money on a ticket and writing a review afterwords.
"If you try to shag my husband while I am still alive, I will shove the art of motorcycle maintenance up your rancid little Cu**. That's a good dear"
Tom Stoppard's Rock N Roll