We can't gush enough about the Antoinette and the service we received there. The staff was so helpful and friendly, including accommodating my husband's serious food allergy (the chef even baked my husband a cake for his birthday! first time he's ever been brought a cake and had waiters sing to him in a restaurant -- usually if he's going to have a cake, I have to bake it!). We were very comfortable in our cabin, and also really enjoyed playing board games in the pretty lounge, basking on the sun deck (the "Romantic Rhine" stretch of cruising with all the castles was really incredible), and swimming in the tiny pool (be warned that it is usually quite cold). We thought we'd be really excited about the movie theater, but we didn't want to see any of the movies being shown there.
The food was great, especially the "epicurean dinner" night. We wished there were tables for 2, but had nice conversations with the other passengers who sat with us (at breakfast and lunch we were usually able to have a table to ourselves).
The itinerary itself was not the big draw for us, the boat was. We did a lot of wandering on our own, and found Koblenz and Strasbourg to be the most interesting towns to see by walking around. Rudesheim was the least interesting of the places we stopped.
The fitness center is small but nicely equipped, with an elliptical machine, a treadmill, a rowing machine, yoga mats, some free weights, a mysterious vibrating platform that confused me, and three stationary bikes, one recumbent. The ceiling is low and the treadmill is a bit tall, so people taller than me (I'm 5'9") would not be able to use it without bumping their heads!
I don't see a place to add pictures to this review, but will post on the forum and link to pictures.
We recommend taking a few days beforehand in Amsterdam and we found it easy to get to the boat on our own; however, arriving in Basel was a little difficult as we were taking the tram to the train station and the tram ticket dispenser wouldn't take paper bills, and it was hard to find a place to get change because everything is closed on Sundays.
All in all, highly, highly recommended. We had an amazing time.