After 15 cruises and over 300 days on Seabourn we decided to try a river cruise, so to be fair my opinion of this cruise is colored by my Seabourn ocean cruise experiences. A river cruise was something we had thought about for the past several years, and had enticed friends who never did any type of cruise to join us. After evaluating the various lines for a river cruise, Crystal seemed to have the best offerings in a lot of ways. The original itinerary was very interesting Budapest to Amsterdam, but due to low water levels it was changed to round trip Amsterdam, less than 2 weeks prior to the cruise - or at least that was when Crystal let us know. To their credit you could either cancel - as our friends did - and get a credit equal to what you paid or go on the changed itinerary and get a substantial future credit, which we took as the changed ports were not places we had been to. If you took the cruise, they would also cover up to $1000 of airfare per person, which worked out well since we had flights booked to Budapest.
We took advantage of the Crystal - included - airport to/from ship transfers on a comfortable coach.
Once we got to the ship, the service from start to finish was top notch. But I need to qualify this, the ship can hold 106 pax, we only had 44 due to the changed itinerary. We had a butler who basically was useless, canapes delivered to the room each afternoon, 1/2 the time after we had left to go to the bar for pre-dinner cocktails. Never offered to pack or unpack for us. Nice guy, but one less crew they need to pay, IMO.
There is only 1 bar on the ship, excluding the pop-up on the open deck where only one day was anyone actually working there (the hard-working bar waiters always went down one level to the main bar and back up). Given the less than 1/2 occupancy the bar area was nice but if at full capacity not sure how easy it would be to get a seat if one arrived late. The entertainment was varied, when we had over nights in port they brought on some very talented local singers / musicians. When sailing (is that the right term on the river??) we had the on-board entertainer, who was interesting and quite a character but more than a few nights we had karaoke with a few drunk pax and the problem is, this is the only bar on the ship so deal with it or go to your room, or to the top deck depending on the weather.
On the ship there are different categories of rooms, unlike on Seabourn that all are basically alike just the deck level determines the category (and deck 5 veranda differences). So I can only speak to what we had, deck 2 not the most expensive. The room was about 200 sq, feet. No walk-in closet, a single sink, but shower was bigger than on Seabourn, but no tub. WiFi is free for all, as are the tours at each port, some worthwhile, others Mhh. No veranda. Window comes 1/2 way down and a screen goes up. Not that useful unless you need some fresh air, IMO.
The top deck is spacious with a lot of comfortable seating and not on top of each other. They have a unique popup bar - although it was rarely used, that can go down to deck level when the ship passes under low bridges. All the deck rails on the top deck can also be taken down - as happened one day when we passed under a very low bridge. The crew who run the ship details really work hard, especially when things like having to take down all the rails, which was not expected and then put them back up after we cleared the bridge. Interestingly their title is "Sailor".
As far as river ships go, we thought the Mahler was the best looking one we saw - and we saw quite a few at different ports - especially how the top deck was laid out. The ship is relatively new and we did not notice any maintenance issues.
Service everwhere was exceptional, but again it is hard to objectively judge since there were only 44 of us. I never waited more than 2 minutes at the one and only bar to have someone appear to take my order, if we were on the open deck someone usually appeared within 5 minutes of us being situated. At all the restaurants we had good service - and friendly, sometimes too friendly, OK I'd like to eat my food now please while it is hot as much as I enjoy hearing your life story - and what we liked was each night the chef prepared a local dish to coincide with the port de jour. We thought the included wines were pretty good. They brought on more wines as the cruise went along. I do have to call out the great people at the reception desk - we had an issue the entire cruise with a bag being lost in airline baggage purgatory and every day they called multiple times for us trying to get the issue resolved.
The gym was very small, laundry room (something I missed being able to avoid as a Diamond on Seabourn) was often very busy. Getting on and off the ship at every port was easy, although they hire local people instead of having their own security people.
In summary, we very much enjoyed our time on the Mahler and it opened us open to trying a Crystal ocean cruise, and if we ever do another river cruise it will be on Crystal.
Comfortable bed and pillows. Good sized shower. Storage was a bit tight. Housekeeping was efficient and personable.