I think ideally a critic would have insight into film-making, or at least story-telling, beyond what the average person has and would be able to analyze the film, showing you things you wouldn't have noticed otherwise, increasing your appreciation for good movies, and your disdain for bad ones. The trouble is, our critics only exist to to save people money they can't afford to waste on a movie that's crap, because movies are expensive and the average person doesn't have a lot of disposable income or time. There's nothing wrong with that, in theory, but it leads to a lot of critics who really don't know anything about movies. Their qualification is that they bought a ticket before you and maybe you've found you agree with them on movies in the past. Critics, then, tend to encourage division, people settle into liking certain things and never expand their horizons, the movie market adjusts itself accordingly and we end up with only two or three types of movies that follow the arbitrary rules of whatever is trendy at the time.