Just returned from a wonderful week-long cruise on Scenic Amber from Budapest upstream to Nuremberg. (The ship spent time in Budapest, Vienna, Durnstein, Melk, and Regensburg, with brief stops at other places -- see below for more details.) Will try to share below what I think might be helpful (without repeating what can easily be found elsewhere online); feel free to ask anything and I'll do my best to respond.
This cruise was August 10-17, 2023, and my wife and I shared a "deluxe balcony" cabin. This was our first river cruise, but we've done ocean cruises with Carnival (twice), Princess, and Regent. Overall level of service, amenities, included stuff, etc. was very similar to Regent, but on Scenic all cabins have butler service. We were traveling with 4 others, and we all thought the food was just incredible and the cruise overall was a fantastic experience. The crew and staff were a delight. This may have been helped by the fact that the ship was less than half full -- we're not sure why that was, but we were told subsequent sailings were more full. The main language on board is English, and the passengers were from a variety of places (largest contingent was from USA, but good numbers from Australia, New Zealand, Britain, Canada, and a handful each from Spain and Belgium). The crew was mainly European and Asian, and were ready/willing/able to do whatever they could to make the voyage a good experience.
As a first river cruise, some things we noticed (apologies to experienced river cruisers, who will be saying "duh", but it may help other newbies): seasickness simply isn't an issue. Sometimes when docking you'll "raft" with other boats (docking side-by-side out into the river, so passengers from one boat will cross over or through another to get ashore). We did this a few times and it was interesting, but not a negative in any way. The ship went through several locks during the journey, which was fun to watch. And sometimes the bridge clearances were low enough that the ships would lower some masts and sometimes lower the bridge (and in our case sometimes close off parts of the upper deck, but not all of it).
Another distinction with ocean cruising: most ocean cruises seem to follow the "sail at night, dock in the day" model nearly every day. On this cruise (and maybe on many river cruises, I don't know) that wasn't the only way it worked. And the exact times in port weren't really published in advance (though they were available if I called). Some days we would stay in a city half a day then being sailing mid-afternoon to the next destination. This can be fun because on a river cruise sometimes it's the river itself, and what you see from it, that's of interest. (And part of Scenic's app is a river guide that will alert you when you're near something interesting and play a 1-2 minute audio describing it.) Examples: on one day we docked early in Durnstein, Austria then left late morning -- some passengers stayed on the ship as it sailed to Melk, but some went on excursions that left from Durnstein then met the ship in Melk mid-afternoon, where other excursions were available. We then left Melk in the evening. In bigger cities (Budapest, Vienna) we stayed overnight. There were also a few stops that were called "technical stops" where the ship only stopped briefly, for example to let off passengers doing specific excursions who would then meet the ship at the next port. Example: we stopped briefly at Brandstatt just to let off passengers for excursions to Salzburg, Cesky Krumlov, and other places. Then those passengers met the ship at Vilshofen, where they got on board and the ship continued on.
We opted to arrive in Budapest a day before the cruise began (stayed at the Marriott, arranged by Scenic), as do many folks who cruise (river or ocean). In this case, this was less necessary, as the ship spent the first night of the cruise in Budapest, so missing the ship is less of a risk. But we're still glad we got the extra day in Budapest.
Each day there was a brief "port talk" about the next day's activities, with just enough info. to help us decide what to do, including details about how much walking, bus riding, etc. was involved. This was helpful. All excursions were included in the cruise fare. Unlike ocean cruises we've taken, only two of the excursions were able to be chosen in advance of the cruise -- our choices for Budapest and Vienna. For the other stops, we made our choices after the cruise began. I'm assuming that with these relatively small river ships, it's easier for them to adjust tour sizes at the last minute. For guided tours, there was an app that would allow your phone to be a receiver for the guide's voice, and that worked well for us -- we appreciated not having to bring along another device on the tours.
Most nights there was some form of entertainment: Hungarian folk dancers, Austrian folk dancers, ballet dancers who performed as well as tried to teach some of us the Viennese Waltz, a "name that tune" contest one night, and trivia on the last night. In Vienna there was a concert just for us at Palais Lichtenstein (beautiful baroque venue), with a professional chamber orchestra, singers, and dancers. Many passengers found this to be very special. All of this was included -- the only thing we spent money on while onboard was my wife's massage (every passenger had 50 euros shipboard credit, and she used up both of ours on the massage).
There were set times for the 3 main meals each day, but there were always other ways to eat (room service or some really good snacks available all afternoon in the bar area). Breakfast included a buffet but also had a menu you could order from. Lunch was similar, though more emphasis on the menu than the buffet. Dinner was menu-ordering only. Wines were often local (as were many of the food options). Each passenger had at least one option to have a more "special" dinner at the Italian Portobello restaurant (which was really just a glassed-off area of the main lounge/bar, but the meal was outstanding).
The ship has just over 20 e-bikes, which you can ask for anytime you like and the crew will have them on shore for you in a few minutes (locks and helmets provided, though we saw few other adults with helmets in Germany and Austria). We also went on a guided e-bike ride (using the ship's bikes) from Durnstein to Melk (both in Austria), which was a great way to see the Wachau Valley.
I initially had concerns about the Danube water levels, but there was some rain before our cruise and things were fine, until the last full day -- we stayed at Regensburg instead of leaving mid-afternoon for Nuremberg, where we were set to disembark the next morning. For our group of travelers, this actually ended up being an improvement, as we loved Regensburg and we weren't going to have any time to do anything in Nuremberg except go to the airport. The extra hour on the airport transfer was worth spending the rest of the day in Regensburg. We got an email just after the cruise saying that Scenic will refund each passenger $75 per person. I don't know whether the low water levels were on the Danube itself or in the Main-Danube canal.
Bottom line: I highly recommend a Danube cruise and a cruise on Scenic.
Please feel free to post any questions you may have -- I left out a lot to keep the post from being too long (which it probably already is, whoops).