The Marco Polo is an old ship but she's been lovingly looked after. She's kept spotlessly clean by the staff. The cabin we had (for 3 people) was a little small (I had the top "bunk") but again it's clean and perfect for our cruise of a week.
It's not a big ship (800 passengers) and that means it doesn't feel impersonal by any means.
The choice of food in both restaurants is amazing - tasty and plentiful. You won't starve on this ship. Free tea and coffee and water available at all times. Never ran out of anything.
Great if not a little bit small for 3 people. 2 would be fine. Shower was great; hot and surprisingly powerful. Kept spotlessly clean with beds turned down every night.