Also, the character model's hands+feet commonly clipped the walls slightly, and sometimes had that odd sliding motion in which the overall limb seems approximately stationary with respect to the surface they're touching, but the actual edge does not, it slides about a little.

I mean... that lighting was really, really good, and I think this is the first triangle-based demo where the surfaces really don't look oddly angular almost anywhere (maybe with exception of the stalactites). But it's a far cry from the hand-tuned look of something prerendered.