Firstly i would like to say that i am not saying this is a new feature or saying that this feature is going to be better than any other game or mod, all I am going to state is that it is going to be implemented into the mod and show how it will change.
Bump Mapping has been around for a very long time, more than likely was around since before half-life 2 was released and has been used in small parts of the game just to give it that little extra feeling of realism when it comes to npcs, props and so on; but wasn't used on many textures at all. This may be because valve didn't want to make a normal texture for EVERY texture that was made, or because the computers at the time weren't able to handle it ( yeah right ).
For those that don't know what bump mapping is. It's a little feature that changes how a texture will react to shading giving it a bump surface much like displacement mapping, only bump mapping will not change the physical shape of the texture but change the shading on it which cal make something concrete look like sand or dirt look like metal.
Here's an example of a texture without bump mapping and the same texture using bump mapping to add a bit of depth to it instead of it just being a flat and boring texture.
Although this is a small change, it can change the game dramatically and almost make it look like another game as valve didn't use it enough to be that noticeable; but they didn't have to use it all over the place to make such an awesome game. Bump mapping is only really good on plain textures, things that NEED bump mapping in order to make it look like it's not completely finished and to give it that little bit of polishing to make it look better for the eyes.
Isn't this Parallax Mapping? You must be asking yourself. well no, they are 2 different features where bump mapping changes the shading of the texture and Parallax mapping changes the depth of the texture by displacing the texture coordinates at a point on the rendered polygon by a function of the view angle in tangent space.