the changes were 90% pathetic repulsive garbage (in your face cgi characters, bad sound effects, changes to editing that ruined the storytelling) or 9% nuetral tradeoff (replacing old background mattes with digital mattes). I cant really think of anything that actually improved except for 1% below:

1)replacing "tractor beam" so its not in english ;P

2)adding that extra 'oomph' to vaders voice in SW (anyone know why it was different? im sure sound technology didnt change that much between 1977-1980)

3)during trench run, when the ships are coming right towards you, they go through the camera instead of cutting to the next shot - this was the only thing that still looked like 1977