PEOPLE who write about art exhibitions often see them before they open to the public. So we are accustomed to friends and strangers asking, “Is it good?” But since “ Leonardo da Vinci: Painter at the Court of Milan ” opened at London's National Gallery in early November, a new question keeps coming up: “Is it worth it?”

At first this question struck me as odd, even shocking. After all, this really is a once in a lifetime chance to see so many paintings by one of the greatest painters in the history of Western art. Some 18 paintings by Leonardo survive; half of them are on view. They have come from Prague, Rome, Krakow and St Petersburg. For the first time ever—not even Leonardo had this experience—both versions of his monumental "Virgin of the Rocks" can be seen together and in the very same room. This makes it possible to compare his different approaches to a single subject; the moods he chose to convey. (The Louvre's is warm and human; the National Gallery's, which was recently restored, looks like a vision from beyond the grave.)

For these reason alone—and there are others—for anybody who cares about art, the answer to the question “Is it worth it?” is a blindingly obvious “Yes”.

But the question isn't silly, and the people asking it aren't philistines, necessarily. The same concern that provokes the question also makes it hard to answer. The show is extraordinarily popular. Everyone thought it would be a success, but few imagined that it would rival a Lady Gaga concert as a hot ticket. Within a week of its opening, those who waited for reviews or were too busy to book, found themselves out of luck. The show, which closes on February 3rd, was completely sold out. In spite of the National Gallery's policy that tickets bought from scalpers (and eBay) would not be honoured, people were buying these £16 tickets for more than ten times that much. Gossip columnists have reported on the fashionable people who are desperate to prove they have not missed out.

If there is going to be a burning hot ticket, how dandy that it's for art. The National Gallery should be congratulated for its decision to hold back 500 admission tickets for sale every morning of the exhibition. Getting one is not for the late riser. During the Christmas holiday, queuing began at 6am. These days lines start forming at 7 or 7:30. Bring a folding chair: the museum's doors open at 10am, and its website warns of a four-hour wait. Those who persevere and get a ticket may have to wait much longer. This is a timed-ticket exhibition to help regulate visitor numbers, so it may be five hours later before one gets in. That is what has generated the “Is it worth it?” and the second thoughts before answering “yes”. But these second thoughts don't stick around long.

This art lover always found Leonardo da Vinci a chilly, remote painter, more appreciated than loved. Seeing his glowing “Lady with an Ermine” and then soon after his unfinished but searing St Jerome changed that. I got Leonardo. Well, better slow than never. Much, much better.

Maybe there aren't queues and crowds in Krakow where the "Lady with the Ermine" usually lives. But visiting the Vatican museum where St Jerome hangs is a nightmare. To get to the art there one must climb the stairs and pass through seemingly solid masses of tourists whose only movement is the tapping of their smart phone cameras as they immortalise one another. In comparison, the National Gallery is relaxing. In other respects it is incomparable. The crafty viewer can hang back or speed ahead to find small pockets empty except for communing with Leonardo. “Is it worth it?” Yes it is.

Read more: "Deciphering the da Vinci code" (Nov 2011)