2nd Movement of a Serenade

I have been working on a serenade for my mom, and just completed this second movement. I was hoping for some feedback, and maybe some recommendations for the final section, where I tried to modulate into D major for a short period of time, but I feel like it just turned into some accented music, and didn't really do much.

Thank you for checking it out

- Ben

Generally, it's just kind of flat. It's relatively rudimentary and jumps around a lot when I don't think it needs to. Keeping one line steady is the fun of the serenade; it's more the accompaniment, heterophonically that drives it.
:21 - Eb vs. D
:26 - C vs. D, with no other chord tones.
1:39 - Crossed voices.
Section at 2:04 - will sound awkward in actuality because of the direct octaves accompanying a lone soprano line, just acoustic things.
2:10, last measure of the system section - D major vs. G major tonic. Careful.
There never really was a modulation in here, from what I here. More like a resolution to a dominant, since it really doesn't last long.
Some of ilv's comments confuse me, especially 5 and 6a, but I think their point is that chord structure need not be so constant which is why a lot of this feels stilted. 
I hope your mom enjoyed it!