Nothing major - from what I can recall, I fixed the wrong cropping in the first quarter of the film (but there was only like a one pixel difference at the bottom, nothing big), Vader's glowing buttons were still blue instead of green in a few shots in v2.1 and those were fixed in v2.5, then I also fixed the color of Ben's robe in the shot where he activates his lightsaber and there may have been some more very minor fixes like that, which I don't even remember. Probably the most significant changes were getting rid of the flicker in the scene where Luke finds 3P0 hiding because R2 ran away and using 35mm scans to restore the missing frames from the shot when Han shoots Greedo.