A good critique will give positive suggestions on making a written piece stronger and more marketable. That doesn't mean that there won't be negative comments and comments that an author does not agree with. However, a good critique should show the author a view of the work looking through a wide lens and from a different angle, neither right or wrong...just different.
A good critique should never be all negative nor should it be all positive because in reality the work being critiqued is not ready to publish so not perfect. Comments stating " I like it" or "it doesn't work for me" are not specific enough to improve on so become meaningless to the author. A comment like " I think the character needs more emotion" or " the climax is weak, can you increase the tension here?" gives the author a starting point to improve the work.
An author should not feel obligated to change an entire manuscript based on the results of one or two critiques unless it will improve the work. The author should consider other points of view when deciding what needs to be revised with a conscious effort to leave the personal and emotional aspect out of the revisions. Developing a tough skin and the ability to cut, revise, and reshape a manuscript without hurt feelings comes with experience but is a must if one wants to be published.
Critiques offered by agents and publishers should be considered slightly more valuable because at this point the manuscript should be almost ready to publish. An author working closely with an agent or publisher benefits from making some suggested revisions for the purpose of pleasing the one who will make the effort lucrative. Even to that end, the author still holds the key to what changes will be made and what remains in alignment with the character, plot, and purpose of the work.
Authors need to find a solid group of critique partners, one or maybe two, that can be counted on to be honest, objective, and noncompetitive when helping to improve a story or article. Relatives, spouses, adult children, and neighbors may not be the best choices because of their lack of objectivity and their feelings of loyalty to the writer. It is better to have a critique partner that is also a writer and one who understands the pieces of a story, a story arc, and character development.... one who can spot a flaw with a manuscript and give suggestions for improvement. Those critiques will help an author grow and improve, and in the end isn't that what we authors strive to achieve?