My EXPERIMENTAL string quartet. What do you think?

Trying to recognize and reject the concept of sonata form by presenting transformations of the same motif's in a continuous dynamic every-changing cycle. Looking for constructive feedback... https://www.youtube.com/watch?v=LlarRvohpI0

I'll be honest with you.

The only thought the piece gave me was 

"why the hell is the ending all octaves".

I mean, octaves could, of course, add some effect (actually we had a talk about it a few weeks ago),

but it's empty harmonically, where at the end of the piece I'd want... even a bit of a reach sound.

Of course, you could end it with just one instrument (which, as I saw you know, can also play two notes at once),

but you used ALL of them and only have one voice going there.

I mean come on who doesn't know this:

That's like one of the most beautiful passages this man has ever written.

Please, add some harmony there.

Unless, of course, you had a reason for that.

Not sure what's so experimental about it, unless you're not using the term in the sense of the genre; that is to say, it might be experimental for you.
Regardless, it's fine as a piece but is ironically too safe. Harmony is preserved in cross voice motion and despite tonicizing different chords within the progression, I hear at as a modular progression. 
Your use of cross rhythms and direct metric modulations need particular attention. While I do hate it when people say repetition legitimizes, lack of continuity is even harsher. This is not a through composed piece and yet many of your sections give the impression that it is, creating this bizarre disconnect between what's heard and what's written.