My money is on him saying morrowind.... While enjoyed morrowind , ive moved on. There have been plenty of games where i really enjoyed one part of the series but ive never understood this extreme nostalgia that Morrowind brings up in people. Move on FFS lol . Same with D2 and D3 .
OT : Didnt the Devs say that the main story wasnt what they focused on. Also there are not alot of game(including franchise) where you can mod it to your liking.
Never played Witcher series but W3 looks interesting enough for me to play