Visually, Infernal looks fairly good. There are many modern features such as bloom, shadows, colored glass, motion blur, environment mapping, reflective surfaces and tons of flashy particles everywhere. There is great attention to detail in lighting as well.
In places, textures are so detailed that you can almost read the manufacturer's name off the guns.
Lighting and shadows are impressive in some places.
Yet with all the eye candy, the game runs fast on a modern system - our test setup with an ATI Radeon X1950 peaked at over 100fps with everything set to Very High. If you drop down the settings and eliminate some of the modern features, you can run the game fine even on an ATI Radeon 9800 Pro. While the publishers' recommendations are bit optimistic in my opinion, I must admit that the game does run even on those systems, but since this is a fast-paced shooter, I'd ask for a solid 60fps in most cases, and that requires a bit more. The YouGamers recommended system can run the game fine without dipping much below 60fps while retaining the shiny visuals.
At the Very High setting, things look quite pretty.
Lighting and shadows is especially detailed.
When you move to medium settings, texture detail drops a notch.
You also lose some of the shading and decals, such as the visible damage to the glass.
Very low settings, shadows are gone...
...texture resolution is down and lighting is simplified.
Note that you'd have to dip to Low settings only on very marginal systems. Even the YouGamers minimum can run the game comfortably on the medium settings at an acceptable frame rate.