All user reviews on the site can be rated. At the bottom of each review, a prompt asks "Was the above review helpful to you?" followed by Yes/No buttons where registered IMDb users can cast their vote.
Please note that "helpful" doesn't necessarily imply "positive" or "favorable". A review can be helpful even if it rips the film to shreds because it can help readers decide not to waste their time or money watching it.
Likewise, to find a review helpful doesn't mean that you must agree with it. A well-thought analysis of a film can still be helpful and shape your opinion differently or bring a novel point of view to light, even if you ultimately disagree with the author's conclusions.
The aim of the 'helpful' feature is to help valid, well-written
reviews surface at the expense of less interesting ones. We think that
our users are ultimately in the best position to decide what's good or
not for them, and that their opinion should be given consideration when
displaying user reviews on the site. If a review with which you disagree is rated as more helpful, this means a majority of users had a positive opinion of the review, and not necessarily the film.