Probably the most notorious difference between the console version of Assassins Creed Unity, and the PC version is the ability to switch from the old Screen Space Ambient Occlusion technique to the newer and better HBAO+. If all this sounds like another language to you, Ambient Occlusion is a technique used by developers to create realistic shadowing around objects to emphasize the depth of field of each scene.
Like many other graphic settings, Ambient Occlusion has many variants. SSAO has always been the standard but it is already old enough to call the grandfather of graphical settings. Back in 2008, NVIDIA introduced Horizon Based Ambient Occlusion which uses a more complicated algorithm than SSAO, but brought a higher definition, quality, and visibility to AO shadowing. Unfortunately, HBAO proved to be very demanding and most games (such as Battlefield 3) rendered HBAO at half the resolution to compensate for the loss in performance. With the help of DirectX 11, NVIDIA reconstructed HBAO+ to be more efficient, and even added more defined and accurate shadows.
Of course, HBAO+ still takes a higher toll in performance than SSAO, but the impact it has on realism and that next-gen feel that gamers so highly crave make it a very reasonable sacrifice of performance. HBAO+ played an important role in Assassins Creed Unity as each of the vast amount of objects can influence the occlusion of light. Below is a screenshot comparison between HBAO+ and SSAO.