Image-Quality Settings
While you can bother with the minutia in advanced-render settings, there are three predefined profiles that do a good job of delivering different levels of game performance for various tiers of hardware: These are aptly named Low, Medium, and High.
The Low Detail setting should be avoided if at all possible. When using the low-profile, advanced-render settings are all set to their lowest values–shadows are non-existent at this setting and the game world is flat due to a lack of a good lighting model. In general, it lacks depth and ambience, which are critical for a game that's supposed to keep your hair standing on end. If your graphics hardware isn't up to snuff, playing at Medium Detail and a resolution of 1280x1024 is far preferable than playing at Low Detail and a resolution of 1920x1200.
The Medium Detail setting really steps things up, turning on all of the advanced-render settings except anti-aliasing (AA). Shadows are raised to the medium setting, which turns them on and makes a huge difference in the game's lighting model, while adding depth to everything. At a quick glance, the Medium Detail setting appears to offer identical visual quality compared to the High Detail setting, but a closer looks reveals that the medium setting's shadows are at a very low resolution and are blocky.
At High Detail, shadow resolution is increased, shader quality is increased, and AA is enabled. The shadow quality is really much better than medium with softer edges, although when a shadow is close to the camera it can still exhibit some unpleasant blockiness. This drawback is something that high-end PC graphics hardware could definitely do better with, and I'm a little surprised the developers didn't make an ultra-shadow quality option for capable graphics cards.
