[simojo]

Recently, I made an Arduino UNO that I showed to have better switching characteristics than a commercial board. It was a great project to help me understand how seemingly inconsequential routing practices can lead to issues down the line.

http://www.simonjjones.com/#/posts/golden-arduino

[achr2]

I enjoyed your post - PCB routing is often an act of 'zen and the art of..' for me and I recently did a similar exercise for an esp32.

[bschwindHN]

You should be able to improve it further with a 4 layer board, as you can have the signal lines closer to their reference planes, and can more easily avoid signals crossing each other and breaking reference planes.