Since the beginning of 2014, there has been a lot of videos demonstrating the realism that can now be achieved with Unreal Engine 4.
Often, these videos showcase a static scene or even concentrate on a single detail: lighting in an architectural structure, the look of rain hitting the ground, or some wet pebble on the beach.
Physically based rendering, global illumination and screen space reflections seem to manage to trick the brain an get it confused between what is real and what isn’t. Even when some artifacts get salient, like reflections popping in and out or changing with camera orientation, we are quick to forget them and find the image very believable.
The Art of Rendering (April 2012)
A description of the different techniques used in high end rendering and the major engines.
The State of Rendering (July 2013): part 1, part 2
A lengthy overview of the state of the art in high end rendering, comparing the different tools and rendering solutions available, their approach and design choices, strengths and weaknesses as well as the consequences in terms of quality, scalability and render time.
(Brace yourselves for the massive tag list hereafter.)