How do you make textures look like the textures used in Amnesia?

[Juby]

The reason why the textures in Amnesia have such depth to them is because they use normal maps and specular maps. Normal maps fake the lighting of bumps and dents. Specular maps define a surface's shininess and highlight color.

In order for you to obtain the same level of detail with custom textures, you must venture and create some spec maps and nrm maps. You can create your own using some image editing tools, such as GIMP.