Are there any consistent flaws with the songs I write, or just anything I could improve on in general?

Chiptune is hard to critique because of the self-imposed limitations.

Your best bet is to use reference tracks. Pick a song you like by an established artist that sounds similar to what you want to make, drag it into your DAW, and compare your decisions against that song each step of the way. Music production is a bunch of different skills that can be practiced and improved, and a reference track can give you a clear goal for each of them.