While there are a lot of sites out there with cruise reviews, a few stand out from the crowd. These are the most used and most respected sites.
CruiseReviews
Cruise Critic
CruiseMates
CruiseMates does not have user-submitted reviews, but they have detailed information about the cruise lines and each ship that will surely helpful in your own research. They provide information about who should be interested in the ship, and who should avoid it, plus information on decor, public areas, cuisine, restaurants, service, tipping, entertainment, cabins, and more.
Cruises Only
Cruises Only has a huge number of user reviews (more than 300 for some ships). They have overall ratings for customers as well as for their own experts. The user-submitted reviews also include some helpful information such as the reviewers age, travel type (such as group), and type of room they stayed in. There are ratings for ship quality, food, room quality, staff and entertainment, in addtion to an overall rating.