1. Replacing the emperor, surprisingly, didn't bother me, though his extra lines DID. Did someone REALLY have to repeat the "Search your heart, you know it to be true" line?
2. Again the boxes around tie fighters were still present, but nowhere near as blaringly obvious as on A New Hope.
3. Again there was flashing during the lightsaber duel, but this time it was more contained and thus a lot less noticeable, unlike in A New Hope where it was outright blinding and distracting.
4. (This might've been a problem in the original as well, but I don't remember) What color IS Bespin's sky? One minute it's blue, another it's an orange-ish hue, and one time it was even purple! Consistency, please! And BTW, SUN GLARES SUCK!
Otherwise, nowhere near as bad as the New Hope disc.
So far, the changes that bother me the most are the audio ones, not the visuals. Adding music to Luke and Vader's lightsaber duel, for instance, just totally took the emotion out of that battle and made it less suspenseful.