Hi @Marc Deflin!
I generally enjoy the mood of the piece. Are the chords in the first A section intentionally bare? Sometimes the chords only have their roots and fifths and it sounds bare to me if it's not fitted to other purposes. I like the D major sections more since they sound more flowing and melodious to me.
Personally in b.16 the viola should be in C# instead of C for a melodic minor ascending, and b.26 cello C# instead of C to prevent the false relation with violin I if you do not do it intentionally.
Also ending it in D major sounds a bit unfinished to me, since it sounds like the whole A section in E minor without clear purpose. Maybe add a smoother transtion before b.55 so that the turn to D major sounds more definite and reasonable?
Thx for sharing!
Henry