We sailed on MV Nordkapp Bergen to Kirkenes and return in February 2016. This ship is in excellent condition, stabilised and during the two short open sea periods the roll was quite gentle.
The ship is heated to about one light jumper/fleece temp.
The food is to die for but substantially fishy. There are alternatives at the buffet breakfast and lunch so don't stress.
As stated the ships are ferries and so have little/no entertainment on board. There are daily talks on various local happenings each morning but I chose to take in the view. Mrs fox enjoyed the briefings.
The weather is B COLD out at this time of year (surprise) so have the good clothing hat and gloves and you will, survive mostly happily
The alcohol cost is outrageous as is the water bottle package. You are allowed to request tap water by glass at the dining table and this is supplied without any problems.
Each day the ship has at least one landing of several hours and you can go ashore. The excursions are very expensive but whatever rings your bell. The towns are quite small so you can self guide easily.At higher latitudes the ice is everywhere on the roads and footpaths so you need some form of shoe spikes/grippers which are available in sporting goods stores. I took a great backslam before I purchased mine.
The return trip Kirkenes to Bergen is same same so as most people do, just do the one direction. We went for the Northern lights and saw them on 3 occasions. Freezing, windy, but magnificent.
One trip worth the expense.