We took three days trip with two nights onboard and one day in Helsinki. We spent ridiculously small amount of money with IKEA-card for 4 people (around 100EUR). A very good idea was to take a B4Large cabin and the Viking breakfast (booking in advance on-line was a little bit cheaper). It was nice buffet with variety of things! Definitely worth taking
The cabin wasn't five stars class, but we didn't expect that. It was clean, spacious (13m2) and comfortable with tv, where you could alsoobserve the sea and all islands we were passing, that was really cool!
We didn't eat any dinner on board, only breakfast. We weren't either interested in partying all night, most of the time we admired views on the sundeck! There were a bunch of different entertaiments for people all age: dance floor, bingo, there was a life music and there was karaoke as well.
Seven hours in Helsinki was perfect and enough to see most important things.
It is a good idea for a weekend, with family, couples, and with kids. But if you expect the highest class of standard you might be disappointed. I woul say it was good+ class. I also recomend to eat dinner in Helsinki before departure and buy some small things for supper, because prices onboard are much much higher and food is worse.