There is a noticeable difference in the lighting and slight subtle changes in some textures but that is it.
As for the save games, I had issue transfering mine over due to the shear number of mods I was using with the original. Best thing to do is remove all mods except the official DLC and Official HD texture pack and do a quick save then copy the file over.
"As a species we evolved with complex communication and sound reasoning, monkeys fling poop." ~ Me
“A person who never made a mistake never tried anything new.” ~ Albert Einstein