IT's a toss-up between Bloodborne and The Elder Scrolls V: Skyrim. I love them both equally but for vastly different reasons.

Both are games I regularly return to and love introducing people to.
Both are a lot of fun (But again, for vastly different reasons)
Both have great worlds and lore and writing
Bloodborne has some of the best gameplay and combat in any game ever
Skyrim is great to just curl up and explore/enjoy on a whim

All these years later, I've not gotten sick of either of them yet, despite their performance-related issues.

I got it all, baby! 

PS4, Switch, WiiU, XBO, PC
Vita, 3DS, Android

Top 6 this generation: 
Bloodborne, Sekiro: Shadows Die Twice, God of War, The Legend of Zelda: Breath of the Wild, Dark Souls III, Red Dead Redemption II