I've read that Holland America has become less of a cruise line catering only to seniors but in our trip 8 out of 10 people were seniors. It was great for us because there were no loud noises, children running up or down, and especially we loved that the music played in the bars and lounges was calm and not loud to the point of hurting your ears as in other cruises so we really enjoyed that part. Also the AC wasn't freezing cold as in all the other cruises I've taken. Stateroom service is also incredibly silent and we noticed our clean room but never the cleaning crew except the main cabin attendant who asked if we needed anything when he met us in the hallway.
My only complaint noise-wise is that the public announcements can't be muted. They sound "only" in the hallways but are loud enough to be heard by an older person in the shower. They start with a chime and then instead of just informing people could now get out of the ship the cruise director went on an on and on about activities for the day at 7:00 am! This made it impossible to sleep in and sometimes nap since she did the same for departure. Not everybody care for those announcements so I think they should sound inside the room and not just the public areas but allow for volume control.
As for the ship, the Maasdam is the second smallest ship in HAL's fleet so you should expect the basics of all cruise ships but smaller. However, it does have a wonderful, vast library with books for every interest (only problem is that it's the coldest area in the ship), a daily summary of news and a coffee shop (extra charge).
There's also a tennis court and a small basketball court as well as a movie theater/culinary exhibition area where there are cooking classes for free.
The spa has some decent daily offers and there's also free tai chi everyday.
There are a couple of pools, the one in the lido deck has a retractable roof so it can be covered if it's raining.
The big con is the food. The first 48 hrs they serve you everything even if it's standing right in front of you for sanitary reasons. However, the situation doesn't improve much after the 48 hrs because you can get your own dessert and bread but most things are still behind a glass so for example you have to wait in line until the omelettes the guy in front you ordered be prepared even if you just want a hash brown. There is not enough people to serve and it makes no sense to have things behind glass that are very easy to serve. The taste is also a disappointment too. Breakfast was by far the worst because it was rather limited. Lunch was a little bit better but still lacking. Dinner had the best tasting dishes but nothing compared to delicacies we've had in other ships. Especially being a vegetarian, I struggled to find options since most of the food includes some kind of meat. They only had one day at lunch with Indian food for example and still more that half of it was meat. This will not be a problem to most people but still the taste of the food is far better in other cruise lines.
Overall, we liked the atmosphere, we had a lot of fun with the seniors which might not be appealing to some people but to us it was a big positive in this cruise. The itinerary was great so if we find a deal with a great itinerary on HAL we'll take it but won't purposely look to cruise with them.
I was surprised after reading this was a lower luxury cruise line. For me the rooms and ship in general were no different from Royal Caribbean and less in some aspects. In my opinion Celebrity is superior by far to it in all aspects.