The only problem with "emo" poetry, per say, is if people rely on cliches that are considered emotional tries rather than constructing their own ideas, thoughts, and emotion in their writing. I've written plenty of poetry that could probably be considered "emo", but it doesn't mean that it's automatically bad, (not that it's good either, but that's for other reasons) it just means that there is the idea that most poetry along that line DOES rely on simplistic, overused imagery with no originality. That's really the only problem with it. Moving beyond that, I don't see why it should be considered any less artistic or valuable.
I think the difference between "emo" poetry and "good" poetry is that "emo" poetry presents itself in a non metaphorical way, with many heavy emotions being spewed onto a piece of paper. "Good" poetry on the other hand is those emotions or feelings, being put into a metaphor like a story and then the reader can extract personal meaning for it. So instead of reading a depressive sad piece, and see that the writer has some issues, one can read a piece portraying the same feeling through metaphor and partially experience the feelings for himself, giving the illusion of a "good" poem. But honestly, poetry is poetry, whether it comes out of a bleeding wrist or one that's never been hurt, it all does the same thing, portray emotion in one way or another.
