Lo,
While not Budapest to Amsterdam, I'll give you my thoughts on the one river cruise we took. It was Belgium and Holland with Tauck Tours (they have private-label Tauck river ships). We went during prime tulip season and during the Floriade (which is a huge horticulture/botanical world's fair type venue that happens in the Netherlands once per decade).
For 'certain' itineraries I MIGHT consider a river cruise again. But, there are pros/cons.
What we liked:
1)My spouse totally enjoyed the experience of watching the river ship go thru the locks.
2)We were able to see many villages/cities (on all-included shore excursions....all those are included and no tours are sold as add-ons) and travel very efficiently (mostly at night when the scenery was not spectacular between cities, then during the late afternoon when we enjoyed the Dutch countryside). 3)The time of year we traveled was too chilly (early spring) to totally enjoy the French balcony or the upper deck, but it was nice to have the full-view windows of the French balcony and the upper deck for photo taking.
4) Nice group of fellow travelers (but average age was probably 10-15 years older than us). We were 56/58 when we took the trip, and several of the other passengers upon learning my age would comment, 'oh, you are the age of my son/daughter, etc.' Nice people, though. Most were well traveled, but just sort of settled into a preference for river cruises (maybe due to ease with age). There were a handful of young couples, some as young as late 20s, but they were attracted to the cruise for ease of travel. Young doctor spent evenings editing his photos (which were fabulous, as he shared them with other travelers).
5) Excellent land tours....incredible local guides, efficient, etc.
6) Unpack once.
7) Turnkey...no $ need in pocket/little planning. Airport pickup/return included.
The cons (when compared to small group tours or independent travel):
1) I like historic, charming, very nice hotels with good views from my room.
2)I don't know if it will be the case on the particular route you are considering, but several times on the route we took, river ships are 'stacked.' What I mean by that is, for example, let's say Viking was the first to 'port,' then Grand Circle arrived, then Tauck, then another brand. When you first arrived, you may be enjoying a fabulous view (from your room) of said city, but when you come back from tour, you will find that your view is into the window of another river ship docked immediately next to yours. Sometimes when departing your ship, the ships will actually open the doors on both sides, and passengers literally walk from one ship, through the lobby of the next, etc. to reach the dock (I sort of enjoyed seeing a smidge of the other brands, at least the dining areas, lobbies, etc.). But, in one location, we woke up really early one morning to the noise of what appeared to be an older river ship with what appeared to be a large group of asian tourists (who were extremely noisy).
3) River ships need to be of a low profile (think fitting under bridges), the typical river ship will have three levels of rooms. But, if you enjoy high ceilings, forget that. While our room was nice and in the mid-price section, it did not feel as spacious to me because of the lack of high ceilings. Tauck's rooms are big compared to many other brands.
4) Part of traveling to other countries is experiencing the local cuisine. All dinners were on the river ship. Food was very good, high-quality with very good service, but it was the exact same dining room night after night. vs. the variety of venues available on land. There were 'nods' to the local cuisine, but it was not just the same as dining in an authentic restaurant with local waiters. Ditto for breakfasts/lunches.
Would I do another river cruise? Probably/maybe...but only if it proved to be the 'best' method logistically for seeing what we want to see.
