Summary
Better lighting.
Description
Tweaks to the post processing, SMAA changed to depth detection instead of color, SMAA upgrades should only apply when you play at higher settings so turn on SMAA High to get the benefit. You might lose a few frames, rain effects have been changed, bloom has been toned down, and generally it's a higher contrast experience. It overrides the base HDR settings, so any map that uses it should be changed and improved.