if I recall correctly, there is *a lot* of stuff that is changed in the early and mid game I would imagine. on one hand, it is great since you can see all the new cool changes made to even the parts that you would think would be left alone since it already came out. on the other hand, for those who already progressed, it kind of sucks because you can't experience it firsthand without starting a new savefile.
I fall into the latter, mostly because I am not a human encyclopedia and I know I won't find everything unless I use a guide. but I am still grateful for the changes in earlier versions.