What is a "poem"?

I'm a little confused right now. After putting one of my poems up for critique on another site, it took the best part of five minutes to recieve responses saying, in essence, that I suck. Now, I don't pretend to be a particularly good writer, and I'm not going to throw a temper tantrum and give up on writing, but every piece of feedback means a lot to me. Which is why I have some questions for you Mibbians about poetry, so that I can hopefully learn how to....suck a little less.

Is there any particular limit to how long a poem should be? The one I wrote was 6 stanzas, a total of 38 lines and it was described as "too long". The person also said that it was "not rhyming or rhythming to be a Poem", but I'm really not sure what that means. Do you?

I'm also wondering about poetic techniques. Whilst writing I tried to mimic the persona's thought process by cutting off sentences with abrupt fragments that additonally completed the sentence in an abrupt manner. I was trying to emphasise certain lines by doing so, but I was told by another reader that "poorly constructed sentences" that were "chopped into sixths" did not count as a poem. (For the record, while each stanza may have been six lines, they consisted of several sentences, not just one.) But is it acceptable to have a sentence broken up into two lines in a poem?

The third person who commented just said ",,,.,.,." Nothing more. Can anyone make something of it?

Another said there wasn't really anything to interpret. It was more intended to be bluntly written, using the last two lines of each stanza to contrast the above four. But he/she said "only vivid metaphor makes a text become real poetry". Does it? Can a poem be a poem without metaphors?

Ok, so I've established that I need to improve my imagery, as I came off as being "flat footed" instead of resigned. Oops. And I should probably work on my maturity, as it allegedly sounds like the work of "wise and old 15 year old" that would "make anyone over 16 laugh". That fifteen year old spent over three hours writing it, and the 16 year old me isn't laughing yet, so I really must be in dire need of improvement.

Guess I'll just have to keep practicing until I get it right ^_^"

Much love,
AllyCat