One of the best movie critics ever, Roger Ebert, was often not very critical of even bad movies he had to endure. He would find positive things, highlight also the negatives and have a clear reasoning behind why he would recommend or not recommend a movie. He would also include in his reviews some commentary about the reactions of other moviegoers to suggest what kind of reaction an Average Joe might have for the movie. Finally, he would judge the movies against their peers -- why would you ever even try to compare Police Academy to Kieslowski's trilogy, when they clearly appeal to different audiences? You could say that he was a movie advisor, not a movie critic.

I believe restaurant critics may be the most varied bunch of critics out there. We all appreciate different aspects of restaurants, from the atmosphere, service and food to just personal preferences. Whereas movies are always "served" in basically the same theaters, only once and to an audience who knows what to expect, a restaurant will have to cater to (pun intended) a variety of different types of crowds and perhaps several times. As a restaurant critic, one should not necessarily let a single bad part ("soup was cold") or a single bad experience ("waiter forgot to bring the check") lead to bad review. And yet they should somehow gauge from a single visit whether the restaurant deserves five stars or one, even if the experience for someone else might be entirely different.

In some ways I would like to be a food critic (I think). I might tell people to "save their money and eat somewhere else." The downside to this would be the inevitable hurt feelings of those who were negatively critiqued. In fact, when I was in France I heard about a chef who committed suicide after his restaurant lost a single Michelin Star. So maybe I would prefer to sample the food and make helpful suggestions (constructive criticism). However, this could be construed as arrogant, I guess.

This reminds me of a writing class I took in which each student had to provide the whole class with an advanced copy of his/her work. During the next week in class the work was openly and honestly critiqued. I was annoyed at a few critiques of my work and defended myself by explaining that I followed the guidelines laid out by the prof. Criticism can be challenging and sometimes difficult to take! And I neither enjoy offending others nor being offended.

A good critic should have a discerning mind and be arrogant (confident) enough to express their findings. Ideally, the recipient would be open-minded and insightful enough to benefit in one way or another. In the real world, though, this doesn't always happen. 

This is an excellent question because it is very thought-provoking and open-ended enough to elicit a variety of responses that reflect personal feelings and experiences :)