I choose Fred Olsen because of the itineraries and because I don't like huge ships (I actually prefer those with around 300 passengers, so Fred Olsen ships are still bigger than I like, ideally).
Boudicca is comfortable and the food is very good - plenty of choice and variety, and the staff are friendly and helpful.
My criticisms would be:
My single inside cabin was very small - not a double for single occupancy, so with the "single supplement", it was expensive.
Extremely expensive WiFi (on other cruise lines I've used it's cheaper or free to returning customers),
Shore tours are usually good, but expensive (I use them because as a solo female traveller, it's not generally wise to travel around unfamiliar places alone),
OKish entertainment (I would be happy with far less and my preference is for classical music, although I recognise that I am in a minority there). The violinist and the comedian on this trip were good. The classical duo gave 2 performances and were a bit disappointing.
The 3 other cruise lines I've used, when selling off unsold cabins cheaply shortly before the cruise, will upgrade those passengers who booked much earlier and paid the full price, so that they don't lose out - even if they are not regular customers. Fred Olsen does not generally do this, unless you are one of their very best regular customers, so you may have to accept that some fellow passengers have a better cabin than you, but paid a fraction of what you did. They don't sell off discounted cabins for every cruise, but it's worth bearing this in mind when you book, and also worth checking their website for these cheap late offers.
Small and expensive for what it was - ie a single cabin, not a double for single occupancy. First cabin very noisy, but change quickly organised