Mont St-Michel-Is it worth it?

That totally depends on you. A number of other factors, such as weather when you go etc., also play into it. I'm sure you will get a ton of opinions from your question, but to my mind, it really depends on you and what you like.

Worth it to you? Like Ray says, that's going to be up to you. But.

The best way to see MSM would be to arrive in the afternoon, spend the night on the island, and take off as the tour buses arrive in the morning. Your day-trip plan sounds kind of miserable to me (again, your mileage may vary).

It's not clear to me how the MSM visit fits in with the rest of your itinerary. It's not going to be easy to get to Normandy form the Rhine, and then when are you going next? You might be better off saving MSM for another trip when you spend several days in Normandy, a beautiful part of France with lots to see and do.

MSM is in my opinion one of those rare moments in travel that totally meets expectations. The best part is seeing the place at a distance. We were there in uncrowded late October; I imagine mid-summer might be a nightmare tourist crush -- but I'd still do it. It is a pretty amazing sight.
https://janettravels.wordpress.com/2014/01/21/mont-st-michel-is-that-a-real-place/

I agree with Adam that it's worth it but definitely better if you spend the night so you get an evening and morning without the tourist hordes (especially in June/July). A lot depends on where you are coming from to Bayeux and where you're heading after that. You could plan to go from wherever you're coming from directly to Mont St Michel with a late afternoon arrival, spend the night and morning and then go to Bayeux for a couple of days before moving on. Getting from MSM to Bayeux involves a short bus ride to Pontorson and train from there to Bayeux, total of 3-3 1/2 hrs travel time.

It's an amazing sight. But after walking up to the Abby and back down and then walking up again and through the Abby. We said that it was like looking at the Rocky Mountains. It is a truly beautiful site, but we really didn't have to walk the walk to appreciate it's beauty any more than you have to climb the mountains to appreciate it's beauty. Would we go again and take a whole day to get there and back from Paris? I don't think so. But that said, it is beautiful from afar. Almost unbeleiveable it is so spectular a site.

I dunno, is the Eiffel Tower worth seeing?
The Sistine Chapel?
The pyramids?
The Great Wall of China?
etc.
etc.
Only you can decide.

That said, Adam is spot-on above. Going as a day trip (mid-day) in high season is going to disappoint. Buck up and spend the night on the Mont. It's worth it. I can not think of any reason why a trip to MSM requires a "tour". It's not exactly hard to find. You really want to get away from the tours...

It's pointless to quibble about the exact date, especially since a large number of the MSM visitors are ... er ... not French vacationers. We were there on July 12, 2015, and it was too crowded to have a sit-down lunch without a reservation. The abbey was as crowded as any museum. But that's not a reason not to go. We are not sorry we didn't spend the night. We have had nicer, more spacious medieval accomodations, for example Perouges, Leuven and Guimares. (We seek air conditioning in summer Europe these days. There are plenty of A/C rooms on the mainland "strip" beside MSM, I'm sure.)

The OP sort of, hints that maybe they will have seen enough medieval streets and buildings during the earlier part of the tour. Depending on their past (and planned future) travel experiences, it's quite likely that they should heed the excellent previous reply to save it (one of Europe's iconic and impressive) for a trip to regional France. That's what we did, making a circle from the western Loire, up through Brittany and Normandy, and back to Paris for a few days before flying out. We could skip, for example, Giverny, because we'd been there on a a Paris-day-trip.

I would suggest that if you are not renting a car, you might not need two nights in Bayeux. It's not that there isn't plenty to see around the Normandy beaches, it's rather the overhead of public transportation, and the need (if you choose) to book escorted outings well in advance. If you take a comprehensive, expensive tour of the traces of the American invasion (as opposed to a more general visit to Normandy, the province ... ) you'll make much less of your independent day by the beaches. Are you using Rick's book? (Highly recommended.)

To my opinion Le Mont-Saint-Michel is absolutely worth to visit.

I know you are going to use public transport but nevertheless if it is possible using a car it will give you the flexibility to visit Le Mont-Saint-Michel in the evening. At that time there is enough daylight and later you can enjoy sunset and the place will be stunningly illuminated. Last early June I arrived around 9PM and the place was pretty much abandoned, totally no crowds besides the visitors enjoying their diner in the restaurants. Coming from Bayeux and driving along Courtils you will see it emerging at the horizon and have to say like Janet it has something special.

With a tour you will join the crowds and there is a risk you don’t get the best out of your visit, but in case with a car I think if necessary it will be worth to trade in some time on the Rhine. Guess you have to bring back the car the other day so why not spending the night there and visit the abbey in the morning before the crowds arrive. There are hotels just on the mainland, but also a bit further away numerous B&B’s offering due to competition good value for the money.

MSM is well worth seeing, and I would even say that from there a short drive to Saint Malo really is a good complement. If you manage to extract a bit more time, it is also a beautiful opportunity to discover further Bretagne.
During the high season, an alternative to staying for the night in MSM is also to arrive early (about 8am) and visit the place before the crowd arrives.

I was very pleased with MSM. I didn't do WW2 in Normandie (just the Bayeux Tapestry, MSM and cliffs in Etretat). I prefer older history. I probably would have stopped in Honfleur but I was planning on some old port towns in Brittany, so figured I could miss it.

I love MSM but agree with Adam. I would only go on my own, arriving 4-5, spend the night there and leave by 12:00 next day. I would never do a guided day tour there when it is packed. Think Disneyland on the busiest day of the year.

I went in September. I read on a tourist sight that only about a quarter of visitors climb to the top to see the Abbey. I arrived in the afternoon, stopped quickly at the TI to find out where to start up the ramparts. Saw the Abbey before it closed then worked my way back down the main street and around the outside some while it was low tide. It never seemed too crowded. I was going to stay for the tide but it was after nightfall and projected to be cloudy (no moon to see by), so I went on to Cancale afterward.

I really wanted to get the omelet there but it was 35 euro, higher for other options - so no.

Thanks for all the comments and suggestions. We have travelled extensively in Europe and lived in Italy for 4 years. We are just not too familiar with this part of France. Have done Alsace and Provence. We have seen lots of medieval Europe. We are looking forward to seeing the tapestry and the WW2 sites. The Forum is great and we appreciate all the help we gotten over the years.

Only you can decide what interests you. That said, and I only speak for myself, I was disappointed. We spent the night just off the island. We actually had a view from our B&B. We spent most of a day on the island. I don't know why I was underwhelmed. I just was. I would have rather spent that day/night to increase my time in Normandy. Or Paris. Or any of the other places we went in France during our 3 weeks there. That's just my opinion.

Enjoy your trip!

I visited Mont St Michel last May and really enjoyed it, it is very impressive,you can take wonderful photos from the top,we walk all the stairs up,it was a great experience,you can rent an audio guide on top.My husband and I drove there,just before you enter the pay parking lot which is 12 euros,there is a big stand selling products of Normandy. (very good),the sales lady told us we could park there in front of the stand as long as we buy something from her for 10 euros which we did,bought some nice preserves and walk across the street through the parking to get the free bus to Mont St Michel. It is incredible to think that this was built without big machines. We were in awe. Normandy is beautiful,try the pommeau,apple cider and calvados...so delicious. And of course the wonderful cheeses (Livarot cheese) The coast is beautiful ,Honfleur is really special.
Good luck and enjoy you trip.
Carolle and Gerhard