The cabin space was small but adequate. Decor was as pictured in the brochures and online, but somehow not as over the top as it appears and on the whole quite pleasant. The bed was very comfortable. There was limited storage space for clothing, and no place to hang a long garment; I'd have sacrificed the desk for more closet space.
Our one complaint about the cabin was water temperature. On 3 separate days we had cold showers; albeit in each case maybe a little late (8am). We suspect that there is a limited hot water capacity. The most offensive part of this, however, was that when we reported it first they questioned if we knew how to operate a shower (we're quite familiar with these controls, and the sink was also cold), and then told by the engineer that it couldn't possibly happen.
The public rooms were nice. I liked the scale of the ship, having just previously sailed on the Oasis of the Seas, and enjoyed being able to walk anywhere in a few seconds.
We liked the on-board entertainment, especially the guest performers. We felt that they were not given a very professional introduction by the cruise director.
The dining room food was generally good; sometimes excellent, sometimes not great. The service was also mixed. Many of the service staff seemed to resent being in a service position - often surly. The bar waiter, Gabor, was a pleasant exception - he seemed to truly enjoy his job - always greeting us by name, remembering our beverage choices and offering exceptional service.
The excursions were generally good. Can't beat ancient castles and cathedrals for North Americans where "old" is 100 years. On the whole, I think Uniworld made a good effort to arrange activities given the timing (Christmas eve, Christmas day). We didn't like being dropped in Heidelberg to shop when the shops were closing at 2pm and having to wait around for the bus.
We were most disappointed by the tour director. We thought he was generally disorganized and claimed to be busy trying to manage lost luggage - not sure why that was his job. On one occasion, the "VOX" box wasn't working and his answer was "stand close to the guide. I guess we were the slow group that he didn't tolerate since in Rudesheim he walked on ahead leaving a few slower walkers on their own to try and find the museum.
My overall reaction: Europe was magnificent, river cruising is an individual taste (I liked the scale, my wife preferred the large ocean cruise ships), but we were disappointed enough in the service on this particular ship that we would likely not choose Uniworld again.