Most people love to talk about movies they've seen, even if it's to just give a thumbs-up or thumbs-down. That accounts for much of the popularity of the tag movie review.
A movie review is an analysis of or commentary on a particular movie. Some sites compile reviews from a variety of sources, others ask readers for reviews and other sites use individual reviews. The tag may have broad usage, encompassing not only movies currently in theaters but also ones that are released on DVD. It will also cover the full spectrum of movies, from dramas to comedies to documentaries.
While one might consider being a movie reviewer one of the greatest jobs around, the quality of a movie review depends on knowledge of film as a whole or the subject matter of the movie.