Random, apropos of nothing:

Bauknecht-Trocken (2005) https://www.youtube.com/watch?v=D8ozOOL-Lxw

You kind of have to know the conventions of demos in general and at the time etc, buuut

The breakdown 2:50 min in with the three paintings by Nero has been living rent-free in my head for over 20 years now, especially that third one with the lingering zoom-in.

Just haunting. 10/10 moment

Trocken - Bauknecht

YouTube

More impromptu demoshow:

Satori-Metamorf (2000)
https://www.youtube.com/watch?v=ex-NaV3w5Ro

Metamorf [Full HD] by Zden / Satori (SK) & Raiden / Aural Planet (PL) [2000]

YouTube

This one is really well known (in the demoscene anyway), but has aged shockingly well:

Blasphemy-moralhardcandy (1999)
https://www.youtube.com/watch?v=1Wsr_oCzlZA

This was "high-res" (640x480) at the time. Most DOS demos were still habitually 320x200 or 320x240.

The textured 3D scenes have aged the most, but even 25 years later I have no idea what some of these effects actually do or how they manage to look so good.

Moral Hard Candy by Blasphemy (pc demo)

YouTube

@rygorous One of my favorites. Loved the AA lines back then.

I still wonder how they did those glowing pipe things, though.

@MikkoMononen Also that final screen background (doesn't translate well in the video) with the multi-layered paralax scroll whatever they're doing.