I grew up in the era of the Amiga and got into computing in some part due to demoes like Technological Death and Unreal. Not sure if 10 years is too new to be considered 'retro', but "Intrinsic Gravity" by Still is my favourite demo ever. It's lots of different scenes that transition beautifully from one to another: https://www.youtube.com/watch?v=-ZxPhDC-r3w