At GTC 2014, Nvidia wanted to show the true capabilities of their recently announced Titan Z GPU by showing off Unreal Engine 4 and what it has to offer in terms of lighting effects. After showing a short piece of rendered gameplay and stripping it down, you can see how lighting plays a very big factor in building the complete picture. Without the lighting effects included in Unreal Engine 4, it looks like a half-finished product. Adding the lighting back in, will give you the finished product as you see above, opposed to the picture below.
We also have a video below showing off Unreal Engine 4 where you can see the potential of the engine 4 for yourself.