This Reshade preset aims to fix the lackluster ambient occlusion in Witcher 3, while also adding SMAA for better anti-aliasing, and slight color corrections to make the graphics look clearer and less washed out.
You can download the preset by going here. The first new mod is actually a Reshade preset which aims to improve ambient occlusion, introduce SMAA for improved anti-aliasing and more. A couple of new The Witcher 3 mods have been released online recently, introducing some visuals improvements to the game and changing some of the soundtrack.