So what makes this piece a harmonica/bass piece and not a basic piano piece? Which is how it reads and sounds.
You're not exploring your instruments' potential or writing for the instruments. It seems like you banged something out on the piano and then said "this would be cool for the weird and underused combo of bass and harmonica".
On a C-harmonica, you have the ability to play any C, three different ways (excluding bends), just about any C-sharp two different ways, any F two different ways! And guess what, they all have slightly different timbres (especially blowing vs. drawing)! And speaking of timbre, that can easily be manipulated by slightly changing the mouth shape, or cupping the harmonica, etc.
And bends! An essental part of harmonica playing (though not with the chromatic harmonica, so much) comes from bending notes. And that gives you oh-so-many possibilitie.
Looking through it, there seems to be little regard for breathing -- though I guess an F here or a C there can be drawn rather than blown to facilitate that. But again, that changes the sound. Which you clearly haven't taken into account.
But, for example, the opening measure. How would you play that? Would you draw the F and blow the D or blow both of them? Since that makes a big difference on how its played and how it will end up sounding.
I agree about the 16th notes.
The unison rhythms are extremely boring.
Measure 40, those thirds are strange, same with the octaves in measure 56.
I definately do not think this works, at all, for your instrumentation.
Chromatic harmonicas aren't rare, I have one as well. Mine isn't four octaves, though.