Don't get me wrong, it's a technical masterpiece, but one of execution rather than innovation.

It's main feature was dynamic lighting and shadows, which it accomplished with dynamic lights, normal maps and stencil shadows.

Dynamic lights and normal maps were nothing new even back then, I remember multiple titles using them, but not this well and not to this extent.

Stencil shadows were kind of unique, they worked by extruding the geometry from the light's perspective, and figuring out what was inside the light's shadow by counting front and back faces.

Unfortunately, since they used geometry, they looked really blocky and sharp, with no smooth edges unlike shadow mapping.

Imo they looked kind of bad, a step down from the beautiful pre-rendered lightmap shadows we enjoyed years before.