I am fairly new here - but this is the most interesting piece I have heard so far. It's the kind of music I like to write. The technical issues have already been addressed for the most part, so I won't bring them up again. To me, your choice of voicings here makes this sound more like a piece for orchestral strings, not a string quartet. I would have more interplay, dialog, and rhythmic variation across the instruments. The first 16 bars have enough ideas for the entire piece. Pass the melody around. stretch, shrink, invert, reverse, and vary that melody a thousand different ways. You've already a lot of this, you just need to "harmonize" the various sections so they coalesce into a cohesive statement.
Brian
