Criticism is a general term covering all sorts of writing which take as a starting point another piece of writing. Poetry is a general term for a writing which intends to produce an effect in itself. Criticism and poetry are often quite different in this way.
Critics sometimes appear to believe that their writing should produce a particular effect however. The effect often is to intend to impress the reader with the critic's thoughts, if not his writing. Good criticism (and I think there should be at best good, not great, criticism, this being a social skill), should make one mindful of the subject of the criticism, which is to say a particular piece or set of writing, and the writer or writers responsible for it.
I am certain I have read good criticism. I now avoid bad criticism. It occurs to me to put my hand to writing good criticism, or the sort of criticism I would like to read. I hope I can justify the effort this requires by entertaining or pleasing my writer friends! Well, at least I can do something to describe a sort of principle which might lead to other principles, or qualifications of our shared experience as readers and writers.
Further to principles, the story is in the telling, not the outline. Criticism should be well-written, which I take to mean that the writing should not distract you from the content/tone/implications/meaning being related. There is no one thing or set of things we can believe poems can or should do, any more than we can believe - and I mean believe, not expect, or wish, for, or dream about - that people should say or feel one particular thing or set of things.
I think one goal I would like to accomplish in criticism is not to complain. Not to complain about what a piece of writing does that I do not like, not to bother with what might have been that isn't. Not to criticise, not to annoy or bother the writer. I would hope to illustrate or lend credence to what is accomplished, to what happens that is worth noting. I see no reason not to share impressions. One can question, certainly, but the trick is to do so honestly - which means allowing the writer or reader an opening to respond.
In the end perhaps criticism must be a selfish act. I have admitted that I hope to write the sort of criticism I would want to read. That is, I have no particular ax to grind. I am not an employee of a University or press. I have all the fame I want as a poet, being perfectly obscure. What do I hope to accomplish? To bring some sense of relief to authors, any authors. To note and notarize. To make sense. To make some small bit of peace.
If you read this blog and would like me to write about your work or a friend's work, please let me know. Any piece I would seek to publish would be sent first to the author for comments, including where I might send my review. I may have suggestions where to send too.