Idina Menzel stars in the upcoming production of ’If/Then’ at the National Theatre.” (Jesse Dittmar/For The Washington Post)

“If/Then” is the most entertaining musical I haven’t seen.

Allow me to explain: the new musical, starring Idina Menzel and created by the folks who brought you “Next to Normal,” has been running in previews at Washington’s National Theatre since Nov. 5, and continues there only until Dec. 8. Because this $10 million production is still being worked on as it takes its first baby steps toward Broadway, where it begins performances in March, reviewers are not invited to see it until Sunday, Nov. 24. Here’s a snippet of one of Menzel’s solo numbers, “Here I Go”:

Let me lay out the unusual circumstance in which this drama critic finds himself: Practically everyone in Washington is seeing “If/Then” before I do. This is not the chain of informational custody I’m used to, but I can’t say that it hasn’t been interesting.

Imagining that I, too, have seen it already — or ignoring that I haven’t — everyone I know is also giving me their own informal review. Some are sending it to me via email, or communicating indirectly through posts on Facebook and Twitter. Some are even offering up an analysis when we run into each other, or talk on the phone.

Some people apologize after I tell them reviewers are being held off until the 24th. I also tell them not to worry; I’ve already gotten an earful. Though there is some conventional taboo about infecting a critic’s mind — some mythic notion exists about trying to arrive at a theater directly from a Skinner’s box — keeping the chattering world at bay is a fool’s errand nowadays. The 19 days between the start of “If/Then” performances and the designated critics’ preview might well be either a millisecond or a decade, for all that Facebook or Twitter care. (In the cases of most but not all other D.C. productions, critics are invited after a handful of preview performances.)

Rather than hem, haw, cup my hands over my ears or seal myself off in a library with “Great Expectations,” I’m doing my customary laps in the digital pool, reading the reactions I come across, listening to the experiences friends and acquaintances have been having at the National. And wouldn’t you know, human beings being human, the responses run right across the opinion spectrum, from pleased to perplexed.

I can’t say that the thoughts I’m reading or hearing are having any effect on me aside from raising my own excitement level; I learned long ago that the only opinion I totally trust is my own. So who’s left to care what the newspaper reviewer says? As a harbinger of what might be waiting down the road, the producer of “If/Then” will, and perhaps the writers and director, if they are open to ideas about where the piece needs to be tweaked. A few remaining ticket buyers out there might want also to know what the critics think — and oh yeah — all those people who already have made their feelings perfectly, or even imperfectly, clear.