Utilizing synthetic scales like this is tricky -mainly cause one has a tendency to attempt to maintain major/minor tonal structures and functions. Sometimes, the chords derived from the synthetic scale can be used in much the same manner as they are in major/minor tonal structures -more often then not, as is the case here, they don't.
So... my thoughts on this....
1. I think you noted at the beginning the differentiation between harmonic structures (your synthetic scale vs. M/m tonality). This is clear in your avoidance of homophonic/monophonic textures. In other words, you decided to write contrapuntally. This was a good choice -and I think it lent itself well to the scale you used.
2. That said, I think you didn't explore the scale or your material as well as it could have been. One of the niceties of composing with a synthetic scale is that you have the liberty to explore more strident tonal relationships built into the intervallic sequences of your scale. So far, there's very little -if any- exploration here. I would have loved to of seen more.
3. The ending doesn't quite work. It seems to waiver in a sort of resolution that is unfulfilled -which the material is in striking contrast with. Again, I think this is more to do with the lack of exploration of the scale itself. You hadn't given foresight into how to resolve the material within the environment setup by the basic scalar foundation. More exploration of the harmonic potential of your scale would fix this easily.
I've always been a fan of synthetic scales and highly advocate their use as an alternate means to tonal writing. When done well, you can present compelling ideas that lend themselves well to musical development and capitulation. Nice work here. Would love to see more!