We were on the Prima this past summer. I had reviews, many negative, some positive. And we were not in warm water ports, sailing from London (Southampton) to Reykjavik, and many of the reviews complained that the ship was not built for cold weather.
We loved the ship and had a great time. Go in with the expectation of a wonderful cruise. If you do the opposite and let the negativity of some reviews get to you and to expect a bad experience, that will become a self-fulfilling prophecy.