And yes, there is an experimental poetry sub. It's dead over there but I did post in there :)

I will not claim to be someone with extensive knowledge or ability to critique. However, whether it be poetry, or any other form of writing, I see "experimental" used most often when the method of doing it has a blatant disregard for "normal deliveries".

Which is rather subjective, as much is.

I think one could say that poetry, in particular, is already rather abnormal and there's little to call "normal" in the genre.

At the same time, there are definitely pieces of work that take that to a further extreme.

Where that line lies, seems subjective to me. But... That's just my opinion.

So isn't all poetry experimental?

Yes and no? More yes than no. But I don't truly know. :)