We have just completed an APT 8 day enchanting Rhine cruise and it was very ordinary from and activity and tour perspective, the ship, crew, food and cabins were all excellent however the cruising and on shore activities were badly organised and managed.
Don't believe all of the marketing materials on these cruises as you only have about 2 days of good cruising and the rest is industrial and farm land in a very busy shipping channels, also the age group of most people is 60 plus.
The on shore guided tours are poor as you are cattle in and onslaught of every ship arriving at the same time and there are many of them and lots of poor guides.
If you have mobility issues I would say don't do it as it can be very tough and no one will look after you if you haven't got some good travellers with you.
Our trip of a life time was destroyed by this cruise and I would hate it to happen to anyone else so please research carefully before investing.
Clean well serviced twice a day by lovely staff the do anything to help you but pokey, no balcony or real space to relax for 2 people.