I agree with some of the above, there were some changes that NEEDED to be made.
Example, exploding Death Star ... it's something that works and was needed. Changing Yoda in Episode 1 (audio and video). Again, something that was needed.
There are other changes that weren't really "necessary", but also work.
Example, adding more ships flying past Yavin to attack Death Star 1, adding more of the fly around of cloud city, etc.
Then there are changes that just don't make any sense.
The changes to the original trilogy this time around (that we know about), the Jedi Rocks, Anakin at the end of ROTJ and Jabba in Ep. IV.