Treat them carefully, because review volume in this industry mostly reflects fleet size rather than quality. An operator running eight ships collects far more reviews than one running two, in both directions. Comparing raw counts or averages across operators of very different sizes tells you almost nothing about which one suits you.
Reviews earn their keep on specifics. A review that describes the guide team, the pace of the days, how the food actually was, or how the operator handled a cancellation is worth reading closely. A star rating is not.
The other thing to watch is that a lot of dissatisfaction traces back to a mismatch rather than a failing. Someone who wanted a luxury cruise and booked a hard-charging expedition ship will write a bad review of a good ship. Reading for that pattern tells you more than the score does.