The hook
A medieval abbey stacked on a rock in a bay with some of the fastest tides in Europe, cut off from land twice a day and floated on the water at the highest ones.
01Why it's worth it
Monks have built on this granite cone since the eighth century, piling a Romanesque and Gothic abbey up its sides until the whole island became one vertical town crowned by a gilded Saint Michael. The setting is half the point: the bay has an enormous tidal range, and on the strongest tides the sea races in fast enough that the mount briefly becomes a true island again. It was a pilgrimage site, then a prison, and it is now one of the most visited places in France, which is the honest catch. The single climbing street is a gauntlet of crêpe stands and packed with day-trippers from late morning on. The abbey at the top and the view back over the sands are still worth it.
02How to experience it
Beat the crowd or don't bother with the crowd at all. Stay overnight on the mount or in the nearest village so you can be up the stairs at opening or out on the ramparts after the last shuttle leaves, when the town goes quiet and the bay does its trick. Time your visit to a high-coefficient tide if you can; the tide tables are published, and watching the water come in is the memory people keep. Guided walks cross the sand flats at low tide, which you should never attempt alone.
The honest note
Mont-Saint-Michel is the most-photographed thing in Normandy and gets the crowds that implies, so the useful advice from the r/travel France thread is structural rather than specific: "every single thing you listed was very touristy, so I'm not surprised you experienced queues… it's more about the atmosphere and the neighbourhoods, not about ticking off overrun sights."
Applied here, that means the abbey at opening or in the last hour, staying on the mainland rather than on the Mont, and giving at least equal time to the coast around it — Saint-Malo is an hour west, and the same thread's contributor rated it among their favourite places in the country.