I think the main difference between original trilogy and KOTOR series would be whether or not the Force has a will - original series treats the Force extremely closely to the concept of Tao (Lucas being a methodist buddhist), without any particular 'agenda'

KOTOR2, especially Kreia, treats the Force more sapiently, and as something that can be killed - which seems to contradict Obi-Wan's original description of it in a New Hope (if the Force is created by living things and binds the universe together, then surely you could only "destroy" the force if the universe and living things in it are gone).

OTOH, you could easily say that Kreia is unreliable, which would make this interpretation simply Kreia's perspective, rather than KOTOR2 trying to adjust canon. Or you could also say that Obi-Wan is simplifying things greatly since he doesn't have much time, and he isn't exactly truthful about other things, either. (And it's been a few years since I played the KOTOR games so I could be misremembering)

It's also fair to say that George Lucas doesn't always follow George Lucas' original vision... (i.e., midichlorians, which certainly depart from original buddhist inspirations). Personally, taking the "original vision" and cleaving to whatever was made first isn't important to me, so long as you can tell a good story I don't mind what retcons/worldbuilding changes happen.