What makes a poem good?

I have been giving this a lot of thought and I've come up with my own definition of great, not just good, poetry:

• If you can read it once, then go back in a different mood or after something in your life has changed and it's like you're reading a completely new poem, then it's great poetry.
• If after you've read it, you look up to find that your view of the world has shifted -- even just the tiniest bit -- then it's great poetry.
• If every time you read it, it sinks deeper into your soul, then it's great poetry.

There are a lot of technically excellent writers around.  While I don't really believe you can have great poetry without it being technically good as well, it's clear that writing skill is not enough for automatic entry into greatness.