This is the question that might have different answers, depending on whom gives the answer. A straight forward explanation, according to our beliefs might be: “good poetry is the one that expresses feelings”. As a consequence, you might think, and we agree, that taking this explanation into account: i) good poetry is like a portrait of feelings, and ii) it is something that has an impact on someone and that results of both the creation of the poet and the eyes of the observer of the piece of art.
Looking carefully to the book “Through the Looking Glass” by Lewis Carroll we will find a poem immediately before Chapter I.
“A tale begun in other days,
When summer suns were glowing –
A simple chime, that served to time
The rhythm of our rowing –
Whose echoes live in memory yet,
Though envious years would say ‘forget’”
We might be wrong but, we think, poetry do not need to have rhymes and certainly needs to make us feel something, in order to be recognized as something worthless.
Also, it “transports” us to another reality, as is the case when the author says: “summer suns were glowing”.