Check out an old but outstanding quick demo DT cartamania did showing what Unreal Engine 4 can do.
The artist is also known for his experiments with photorealism from the engine:
This is a quick demo of Emily model testing the subsurface scattering in unreal engine using profiles and shaders, once you learn how it’s made you can use it for any character you want, as long you have the shaders and the texture properly setup, you can get the most realistic result out of unreal engine 4. The purpose of the demo is to showcase what you really you can achieve with Unreal once you have everything setup properly.
Make sure to check out more of his experiments here.