I guess it's a combination of several things:
- How it feels like an actual light illuminating the scene instead of just a cone mask like in a lot of 2D games. It might be the blending of the cone's edge idk
- How analog it is with the little flickering when low on battery
- The smooth turning of the light beam with the mouse accompanied by the character's sprite changing orientation. This just works
- The crisp click and clack audio when toggling the thing
There may be value in implementing some sort of ray tracing like the one in Darkwood, but that's another beast.