I've spent a few minutes exploring the new version, and I really like most of what I see! However, there are a few things I miss from the old version, and a few other things that I would like to see added. As a disclaimer, you may have already put some of these features in there and I just didn't see it or find it. If so, let me know where to find it!
Things I miss from the old version:
Ability to change speed of midi notes movement.
Ability to change the opacity of the particles.
Ability to add my own image to the notes.
I liked the light effect (where the notes meet the keyboard) better on the old version. The new version kind of reminds me of fog or haze, and it's too large/wide for me. Perhaps there could be different styles of lights that one could toggle between?
I also liked the shape of the notes in the old version a bit better. Just personal preference, but I like my notes a little more square than the new version can do.
A few different note textures as options. (I really like that you included the texture you did, thanks for that by the way.)
Ability to modify turbulence/randomness of the particles.
Things I love:
The new particles. I really like the fog effect of the particles, too.
That it works on Windows.
The app in general! Thank you so much!
Feel free to do what you like with my suggestions.