I caught this while I was gonig through - most of the monster names, while I knew were changed, I didn't care since I couldnt really remember the original. Although I did prefer Imps over Goblins or whatever they're called in origins. And I did prefer Corneria over Cornelia. I'll list all the name changes of locations and people I can think of.

Corneria -> Cornelia
Lukahn -> Lukin
Temple of Fiends -> Temple of Chaos
Elfland -> Elfheim (This one was an improvement, I think.)
Kary -> Marilith (I think)

I know they renamed Mt. Gurgu something. I can't remember what though. But as you were wondering, the Mystic Key is still the Mystic Key. And Dr. Unne is still Dr. Unne. (Actually, you'd be suprised how much the same the two are - I used the maps on Unne's site from the NES version to help me through this one.)