What you did was use you V/vi chord as a pivot chord to center around D instead of E-flat. You got back to it by using the steps of a chromatic line.
The beginning was promising. I think you missed out on a lot of opportunities to change the style while you were playing. it increasingly grew monotonous as it mostly the same kind of texture throughout, with exception of the beginning.
I don't know what smaller parts you could be talking about here. If you're talking about any sort of off-modulation, I could maybe see that but not to the point where I can't observe the whole. Analytically speaking, the whole just doesn't really wow me. While I can't say it doesn't sound nice generally (with exception of a part around 1:47 where you clash B-flats and B naturals in your V chord) it felt like an awkwardly executed sonata form. If you were going to composer off of it, I think this gave you a great starting point, but as it stands, it falls flat for me.
I hope this helps:
1. First you create the tremolo (TG tools plug-in: easy tremolos).
2. Move the note you want in the other staff:
Hold “Alt” and “Shift” (Windows) or “Option” and “Shift” (Mac) (*no shift in Finale 2014).
Type the up or down arrow key (depending on which way you want to shift the notes)