The first Change I want to talk about is the new Darth Vader kills the Emperor scene. This powerful moment where Vader decides to save his son by defeating the Emperor is now ruined.
In the original scene we see Vader quietly debating what he should do, but now he has dialog. Before he grabs the Emperor he says No and continues to say No as he throws him over into the center of the Death Star. The link to this clip is below, I wasn't able to embed it.
The next change is Obi-Wan's Krayt Dragon call form Episode IV. If you watched the original you know what the call use to sound like now it sounds like some drunk guy. Link below.
Those are the two changes that bothered me the most. The others aren't that bad.
The Phantom Menace now has a CGI Yoda rather than a puppet Yoda, which doesn't bother me and Greedo still shoots first, which I've learned to just deal with.
I don't know if Lucas knows that he doesn't need to change the films. We loved the films for what they were.