An article by poet Peter Meinke, found in The Writer magazine from 1999, offered six criteria for judging a poem to be "good."  Here's a synopsis of his list:

1. A good poem withholds something from us at first, yielding its secrets slowly, like a lover.  Poems don't "tell" or supply answers--they're not lectures or sermons.
   
   
2. A good poem surprises and satisfies. But after the surprise, the good poem often seems inevitable. (Meinke says we react this way: "I knew that, but I didn't know I knew that.")
   
   
3. A good poem sounds special--either melodious like T.S. Eliot or Dylan Thomas, or homespun like Robert Frost, or jumpy like William Carlos Williams, or playful like e.e. cummings.
   
   
4. A good poem is memorable. Are there lines you can recite from memory? "For God's sake hold your tongue and let me love," "Batter my heart three-personed God," and "Come with me and be my love" have the ring of eternity in their saying.
   
   
5. A good poem speaks to the unanswerable questions. It can do so mostly by using images rather than logical constructions. Part of why we know this is because we use poetry to mark the major turnings of our lives: birth, death, love, and celebration.
   
   
6. A good poem fulfills its promises. What it sets out to do--musically, visually, emotionally--it accomplishes.