Just in the cityscape flyby there are fewer screenspace reflections. The distant trees are sprites instead of polygons. The shoreline and the buildings and structures along the shoreline are more detailed. Higher resolution textures on many buildings in the preview. Ships flying by have higher resolution textures (poly count is the same though). Waterfall textures and effects more detailed in preview. On release VTOL taking off from roof has simpler smoke/exhaust effect. LOD and mipmaps on tree's on Headquarter roof drastically reduced in quality as you approach for a landing. All objects on roof have lower quality mipmaps. Very stark popping transition from low to high quality tarp seen in retail version, but absent from preview version. More stark transition from low quality to high qualty textures especially on tarp to the right side of the roof landing area. LOD & textures on the grate on landing area is blurry and less detailed at a distance. Significantly less exhaust coming from vents around the roof. Once on the roof fewer floating vertical tall buildings/ships when player glances in the air in the final retail version. Fewer reflective water puddles as you approach the line up of people at the security checkpoint on the roof. Fewer people on the roof. Lower texture quality on everyone including all the Vekta guards and civilians. Fewer drones flying around when on the roof, need I go on?
Preview
On release
Now for most of these things its unlikely this was intentional on the developers part, but likely mostly a result of an uncertainty at how much memory bandwidth would be lost due to going with a unified memory solution.