If you want to get a feel for what the MS Marco Polo might be like as a passenger, Google the documentary series "Mighty Cruise Ships" and look for the episode featuring this ship. The programs are 60 minutes in length (shown on The Discovery Channel in Canada) and you should be able to watch it online. The ship could be described as an older smaller explorer-type cruise ship and is not sold as a 5-star luxury cruise experience (such as Holland America or Princess). It would depend on what your expectations might be as to whether you'd enjoy a cruise on this ship.
As a comparison, you could also watch the recent episode about the Viking Sea itinerary in Norway to see the advantages a smaller ship has in sailing some of the fjords and coastal areas. Hope this helps you somewhat. The Cruise Critic website, as mentioned by another poster, is also a good resource.