That would be a limitation of Pico-8. The resolution is locked at 128x128 and it cannot be changed. The game runs at 30 FPS, which makes the faster notes a bit of a blurry mess, I agree. It's also possible to code the game to run at 60 FPS, which could make the symbols more readable. I'm actually wondering why I didn't start with that speed instead of sticking to the default 30.
You're right about the game being pure RNG. I wanted the "stages" to have their own uniqute symbol combinations, a few per stage and the game would just pick one of them every time it was time to spit the sequences out, but I ran out of time to do that for the jam without breaking the code. That would have at least let the player get used to certain patterns if they got stuck to any particular stage for very long. Right now it's more like a reaction test than anything else.
Maybe a better way to do the symbols would have been spitting out... let's say 3 symbols one after another in a sequence, have the player hit all of them for a "hit" and after a few "hits" the story would progress. And instead of the symbol bar, I could have had the symbols maybe appear randomly somewhere in the screen space and have a circle shrinking around them to indicate when you're supposed to hit the key or something. The range for difficulty options could have included the size of the circle around the input symbol, the speed the circle is shrinking and the amount of symbols you need to get right to progress. A much better range of modifiers than what the project currently has.
The end screen animation I'm very miffed about, because Pico-8 is very limited in what you can have in it. It's a fantasy console that is made to have limitations by design. That includes the sprite sheet. I wanted to draw and animate something special for the ending, but there simply wasn't any sprite space left nor did I have re-usable sprites that would have fit the scene. I could have perhaps tried to squeezed every 8x8 pixel square together and optimised the area to get more sprites, but since I'm a complete beginner at coding and making games, that would have required so much more time and effort than I had available for the project. That is why there isn't any special ending and the re-purposed menu selection just kind of pops there and covers up the monster girl.
Saying that, I must admit, while I was putting the game together I felt like literally any other program could have been much better suited for what I wanted to do, but the few days I had to develop the game, I chose Pico-8 because Lua felt like the easiest language to learn in such a short notice and the program, while limited, contained everything from sprite tools to sound editing tools in it. In hindsight that very much got in the way of the visual side of the project.
What I find surprising is that many people, not just the people commenting here, seem to find the game really difficult and an exercise in frustration. Even if the stages are very short and only require 10 proper symbol hits to progress (unless you get progress deleted from missing symbols) I suppose all the testing I did to see if the game runs without breaking up made it feel too easy to me.
Thank you for the feedback though! This is all good stuff to keep in mind in case I decide to fix the issues in the project after the game jam.