I'd say the technology is the least impressive part of it. It feels like 303/acme from 1996. Only on gigahertz machinery instead of a 486. and using hardware acceleration for very basic 3d effects, rather than software generated texture/env mapping.

But hey, kids these days.

I'd say the demo itself is incredible. It only became better when I realized it was WebGL

What else is supposed to be impressive about this?

Even that's debatable.