What places/landmarks/npcs/… did you come across that were in previous Diablo games?
I found the hidden camp from D3 act 2 the other day. Which was a nice find, since unexpected.
location
directly north of the Denshar WP, east of Gea Kul
story related finds
…and obviously Lorath as well as old Meshif from Lut Golein in D2
There is a quest in Zarbinzet that involves Johannas apprentices. (Crusader from D3)