We’re most familiar with Viking Ocean and they are “virtually” all-inclusive and no surprises.
All food is included in the fare including the two special restaurants.
Unlimited wine/beer is included with all meals. These are good, but not awesome wines and beers. If you want higher end wines, beers, or liquor there is a “silver spirits package” for unlimited higher end stuff including cocktails. This seems fair to the folks who aren’t big drinkers, while offering something for those who are.
They offer prepaid gratuities as well. This gets distributed to all ("This charge will be shared among the onboard staff who helped support and provide your cruise experience, including the waitstaff, stateroom stewards, buffet stewards, galley staff, laundry staff and others”). As much as we really liked our stewards (you kinda get to know them on along cruise), it’s nice to see the tips distributed to people with less facetime who might not get tipped as much in other setups. On the other hand, I’d personally prefer just folding this into the base price, but that’s not how the world works apparently.
Finally, excursions are an extra charge - beyond the included ones. These are also prepaid (if you wait to purchase them until the cruise most of the good ones will be completely booked and unavailable). So this is another upfront charge to decide on, but won’t be a “surprise”.
So if you are looking to avoid and end of cruise surprises, Viking provides this. There is absolutely zero upsell for anything. There really isn’t much for them to upsell - though there are a couple of shops onboard.
When you are shopping for cruises it’s very easy to know what the cost will be for a Viking cruise. It’s all spelled out upfront with no surprises built in.