What makes a poem good?

I guess my lack of formal poetry education is showing here, but I think the original question was less about understaning the writer's intent , I usually "get" most poetry. What I wanted to know was why certain cliche or what I thought was kind of a commonplace poem received accolades and others which I feel show much deeper thought and complexity were ignored.

Is it the particular author? The subject matter? (And as an aside on subject matter... I often see when someone writes about some tragic occurance in their life... they almost universally garner positive comments, no matter how badly written.) Does a rough or tragic life make for a better writer?