Tracktion Waveform here. So far I'm amazed by what you can do with the free version and vital synth.
Yeah, on DOS I think. I remember the graphics being pretty smooth for the time. I couldn't really say it made me feel like Doom in 2D, but maybe I never thought about it that way. My memory is a bit fuzzy but I think it felt a lot slower. I think my install was shareware - I probably never played it through to the end because of this. edit: the linked article confirms DOS and shareware.
Since the first lines of your linked site mention SOLID and design patterns, you're already onto the right stuff there. That's the framework side of things. Beyond that, I advise you to go study the advanced features of your preferred language so you know how to code "correctly" and idiomatically in that language (although not in a way that obscures intent). Then it's perhaps a mental hurdle to open your repos and know that all code has imperfections. Opening it may indeed help to improve it - code review is arguably the single most useful practice in code quality.