A friend tweeted me the other day about a show she’d just seen: “That was probably my best night in the theatre ever!”

Since she has also seen the current Menier Chocolate Factory production of Merrily We Roll Along six or seven times already – to my mere two – I sought clarification: surely it isn’t better than Merrily? No, it wasn’t. “Not saying best show,” she replied, “but I had best night out!”

That’s a subtle distinction, of course, but I know the feeling. You can sometimes have the best time of something without it necessarily changing your life.  And just in case you’re wondering, the show that had produced this ecstatic reaction was The Book of Mormon, which she’d just seen at its very first preview.

So if that’s anything to go by, word-of-mouth will already be transforming this show into the phenomenon it quickly  bccame in New York. Last week I interviewed Brian May, whose own West End phenomenon with We Will Rock You is now in its 11th year and as he perceptively noted, “The secret of the show’s success is very simple — it’s word of mouth, the strongest force known to man.”

Getting people talking – and keeping them talking – is what’s necessary. Marketing is the first stage — and the blanket advertising coverage is certainly helping with that. (I saw a London bus advertising ‘now in previews’ the day before previews actually began). But it is the show itself that will keep people talking, and that will do the marketing job for them.

I’m not sure I could put my hand on my heart and choose just one evening from the numerous ones I’ve spent in theatres over my life to singe out the best I’ve ever spent in one. I’ll never forget the great rush of pleasure that the National’s Guys and Dolls gave me, on the numerous occasions I saw it in the 80s and then again at the end of the 90s, or the puddle of tears that Next to Normal reduced me to each and every time I saw it on Broadway a few years ago. But I’m more likely, if pressed, to single out moments; transforming (and transformative) scenes, perhaps mere seconds, in shows that have pressed themselves into my memory forever.

Just to cite two examples: there was a tiny moment at the end of the first act of the last Broadway revival of Nine, where Antonio Banderas’s Guido is on a beach with his younger self. The little boy is playing with sand,and as he pours it, Banderas rushes to catch it. The moment was so heartstoppingly beautiful and articulate about how life pours through your hands before you know it that it absolutely encapsulated the agony of the show as a man looks back on his life’s choices.

Again, at the end of The Baker’s Wife, Stephen Schwartz’s musical about a straying bride who leaves her devoted baker husband for a younger man but returns to him at the end of the show, there’s was a heartbreaking moment that closed Michael Strassen’s 2011 fringe revival at London’s Union Theatre, as they kneaded dough together silently – they were together again, but there was a chasm of hurt between them.

I could probably come up with a hundred more moments like this that have wounded and/or exhilarated me to burn themselves into my consciousness forever. The fact that it is wounding moments that usually do this to me probably says something about me, and even as I write those words, I am thinking of dozens of moments in Sondheim musicals that have done exactly that, from Judi Dench’s devastating ‘Send in the Clowns’ in the National’s production of A Little Night Music to Clare Foster’s current extraordinarily poignant ‘Not A Day Goes By’ in Merrily We Roll Along at the Menier.

But Sondheim also, of course, provided the ultimate line about how life has to be about more than moments: “Oh, if life were made of moments / Even now and then a bad one! / But if life were only moments, / Then you’d never know you had one.” So shows need to be more than the sum of their parts.

And seeing A Chorus Line again last week, in the pin-sharp revival at the London Palladium, I was reminded again of just how great this musical and production are to be just that, and how absolutely indelible Michael Bennett’s thrilling staging was and is. Other productions that feature in my personal pantheon of greatness include another Bennett directed musical Dreamgirls, Nicholas Hytner’s extraordinarily vivid and heartbreaking revival of Rodgers and Hanmmerstein’s Carousel at the National and the original brilliant production of Maury Yeston’s Titanic on Broadway.

But oddly enough, it’s easier to come up with the unforgettable duds than the shows that glow in the memory with fondness like those. As I previously wrote here,

Flop shows aren’t born; they are made. And mad as well as bad. But often truly unforgettable, in a way in which the merely mediocre erase themselves gently from the memory bank. No one who ever saw it, for instance, will ever forget The Fields of Ambrosia, and its immortal corresponding lyric, “Where everyone knows ya”.

But my favourite moment, quite possibly of any musical ever, was the song sung by the travelling executioner’s assistant after he’s been gang-raped in prison: “If it ain’t one thing, it’s another.”

That’s an all-time classic for me. No wonder that Paul Taylor, reviewing its short run in 1996, dubbed it “a reprehensibly enjoyable new musical”.

He also wrote, “The second half of the show left this critic weak with bliss as it trampled over good taste and political correctness like a herd of bullocks.”

What are your greatest nights in the theatre? And worst? Please share them below!