It's 12 years old now, but I am still extremely impressed by this 64k intro https://geidav.wordpress.com/2013/04/14/making-of-turtles-al... and also by this 4k intro https://www.youtube.com/watch?v=_YWMGuh15nE :)

And overall this website is extremely interesting with tutorials and code and great explanations https://iquilezles.org/