For those interested in a comparison, let's look at the differences between Oceania and Princess. We were on the 18-day Dublin-Copenhagen segment. This was our first cruise with Oceania. We are elite with Princess. We chose this cruise because of the itinerary: Norway and northern Russian ports.
Oceania has considerably less merchandising pressure. There is no crew of photographers. The crew seems under less pressure to sell extras. There are no "cruise ship art" events. Speciality coffees and sparkling water are available without extra charge. Speciality restaurants are available without extra charge. On the other hand, the cheapest bottle of wine on Oceania is about $10 a bottle more than on Princess. That generally put wine above what I was willing to pay.
The ship felt less crowded and there was never a problem finding outdoor seating (although the Northern itinerary may have had something to do with that). 650 passengers instead of thousands does make for a different (and pleasant) experience.
Entirely acceptable. The location was excellent, and the noise level low.
We found a cab. Considerably cheaper than the Oceania tour and much more flexible. I'd also suggest renting a car (do so in advance). Even if you are nervous about driving in the UK, traffic on Shetland Island is light.
There is a local company at the dock that will sell your a cruise up the local fjord at a reasonable price.
A good walking city.
Don't book a ship tour. If you want to go to Mr. Floyen, you can book a ticket in advance and save a lot of money (https://www.floyen.no/en).
The cruise to Flam is delightful. The town itself isn't. I wouldn't recommend the pricey railroad trip, but if you do it don't take the ship tour. You can book a ticket in advance or buy one at the town when you arrive.