That's some pretty clever use of existing low-demand rendering technologies in order to achieve better visuals. There are only 2 small problems. At no point too many polygons are displayed which may diminish how impressive this actually is. The only moment where there are quite many polygons, that's during the display of the terrain map. You can see how fog and drawing distance are used to save performance. The other problem is that some of the effects are very limited. e.g. the skybox display is pretty cool (when the stuff rotates in a psychedelic way), but in reality that's just rendering texture on the back and using polar coordinates.
One thing I am genuinely impressed with, though, is the fact that lots of these textures look like high res. I know that the Expansion Pak adds another 4 MB of RAM and this is a pretty impressive display as one can do a lot with 8 MB of RAM/VRAM and compressed texture formats. And the reflections are pretty impressive, too, as there are some new techniques (at least new compared to when the N64 was actual) which make reflection rendering much faster.
So altogether I think it's a clever use of technology, but a bit hard to apply for practical uses as only a limited subset of these things can be used when they are used all together. Basically if you tried all these things at one, you might experience lag. I think that some of the games utilizing the Expansion Pak came pretty close to this stuff though.
Also, that song in the background is what Dubstep should sounds like. <3