I did the Rhine/Christmas markets cruise over Christmas 2017. This was my second AMA cruise and I was a bit disappointed.
First, the staff was, for the most part, very good. It was clear they all had a touch of "senior-itis", this being their last cruise of the season and they were all going home soon. Still the bar staff was friendly and attentive. The restaurant staff seemed to be in a bit of a fog, but it all got sorted out when I had a brief conversation with the Maitre'd.
The food quality was the most disappointing. My first AMA cruise, the food was wonderful. On this cruise, it was mediocre. Many dishes were overcooked and most lacked seasoning. The flavor was just blah. It was all edible, but certainly not the gourmet food that AMA claims to serve (and what I had experienced on my prior AMA cruise). I don't know if this reduction in quality is a result of cost-cutting or if the chef on this ship is just not as good as others in the fleet.
Cabin was small but workable. Very clean and my steward was very attentive. He was probably the best crewmember with whom I had contact.
Shower was great. Good water pressure and always hot.
Room was quite cool (I like it that way), but people who have issues with the cold might want to consider a room on a higher deck - I think being right at the water line makes it colder.
Large city with lots to offer. Largest cathedral in Europe. If the weather had been better, it would have been nice to explore more.
I took the excursion to Heidleberg, which was very good. Old city with magnificent views and a wonderful castle.
Embarkation port. Lovely city with wonderful museums and architecture. I would recommend arriving (or departing) a day or two early so you can see this beautiful city.