The true value of critisismIts rather easy, and entertaining, to be negative. Many popular critics exist who's main goal is to tear down terrible enterprises. Its enjoyable stuff, and very funny in the right hands. The true art, however, is to explain what is good about a film.
The ability to express, in an articulate and interesting way, what makes a piece of art worthwhile is magical. Look at Amadeus, where we have the beauty of Mozart's music laid out for us in such a way that enriches the experience. At their best, a critic should be able to provide ways of seeing a piece of art that you were unable to before. This is one of the reasons why I love film spotting, a film podcast from Chicago. Both critics are able to explain very well what makes a film worth seeing, in such a way that makes me want to watch it again, so I can appreciate the things they see that make it special.
We will not always agree with critics. Many things are subjective, and while there are objective measurements one can apply, how you rank them may vary (I might prefer a beautifully crafted shot over a carefully constructed narrative, for example), but a good critic should allow you to understand why they have taken the position they are at, even if such a position is not true for you.