A critic's writing, be it a "positive" or "negative" review, has as much power as the reader gives it and ultimately does not undercut what a work of art is or what it may be worth culturally. The way in which a critic frames their thoughts allows them to step into the role of a connoisseur, who is a type of authority, claiming their ideas and grounding them in art history, literature, mass culture, or otherwise. Historically, art had and continues to have an institution behind it maintaining what is important, be it within art making itself or the criticism that surrounds it. In fact, there was a moment in 17th century French history where in order to create or assess the societal value of a painting one had to be a member of the Académie royale de peinture et de sculpture (Royal Academy of Painting and Sculpture).* With the advent of self-publishing, writers outside this institution gained the ability to assert themselves to claim credibility in order to share their thoughts on art, leading to the beginning of the dissolution in power and control of the academy. Some centuries later artists working within movements such as institutional critique began to utilize the critical spirit in their work, creating art that at its core could be defined as "academic." One may think that through the absorption of the critical impulse there would be a parallel rise in acceptance for the unaffiliated critic, however, in 1996 there was a blow to the critic's authority when Artforum decided it would be the final year they ran a worst of" section alongside the "best of" in their year end wrap up issue. The "best" and "worst" of column lasted 3 years, starting in 1994, and was cut due to mounting pressure from galleries and art dealers. But, what is so terrifying about the "worst" and what does it mean to look at an object and deem it as such?
Repulsive, upsetting, abhorrent; these are three words that help categorize the idea of the "worst" and the emotions that accompany it. Conventional contemporary criticism tends to skew towards the "best," or a more positive experience in art, allowing for the "worst" to feel somewhat unestablished (most likely in an effort not to offend anyone). By grappling with what constitutes the "worst," an idea that is abstract by nature, the critic is forced to foreground a negative emotion that is frustrating to feel and even more difficult to communicate. To make sense of such an experience the person looking at the work must think critically to understand its internal logic, a method of recognizing a work of art and weaving one's understanding of it to their own unique engagement. We truly can't know if a contemporary artist's work holds any cultural significance until it is one step behind us historically, all we know is the immediate impact of how the work is received by artists and critics. Much of the time the work that challenges the dominant fine art tradition was torn apart by critics who were unconsciously supporting the institution of art; an easy example of this is Marcel Duchamp, who was shooed away from the Salon when he first showed the readymade. Critics called his sculptures "immoral" and "vulgar,"" and then a sort of crisis ensued that made people question why this artist was able to elicit such a strong negative reaction. Critical conversations about "bad" art can linger after a negative review, but said review holds the most value when the show is up, once deinstall happens the writing is no longer relevant and often forgotten.
The art critic is not meant to be an expert, their writing serves as a first thought, an entry point, and is rooted in their initial internal understanding of the art work they are making a judgement about. This notion is most relevant when thinking about gallery exhibitions involving younger or lesser known artists because their work is really in its essence too new and not yet culturally understood but, by invoking critical conversations, the critic helps society understand the value this work may potentially have. Criticism finds its value in the conversations that follow a review, whether you disagree with their words or not you are still talking about their opinions to clarify your own beliefs. The way in which a critic advocates their thoughts to claim credibility can range, as some writers may choose to back their ideas with their words while other critics will simply speak with certainty. A hallmark of the latter approach is that it has clear ranks, such as saying how many stars out of five an exhibition may receive, and argues their claim to criticism through this. Falling back on a ranking does not declare a sort of rightness, nevertheless it does allow the reader to quickly grasp how the work of art is received by the writer. Personally, I've never found it particularly helpful to assert my opinion this way so I will not have ratings associated with the reviews I will be writing. The thoughts an exhibition may inspire can range, but ultimately how "good" or "bad" it is to the person writing criticism, that's a question of taste.
* It is important to note that French art history is still relatively academic while American art doesn't have an academy in the same way, though there are certain programs and institutions that act the same and perhaps have even more centrality. If you are interested in learning more about the history of criticism I recommend watching this lecture by Jason Farago.