For me it's Diablo II. Granted I've played my fair share of D2 since launch, and also recently on a private server with a comrade from hexbear, but I still feel like years later the game didn't grab me as much as D1 did.
Granted I don't hate D2, but for a game that I keep coming back to, D1 takes the prize.
Sounds like the Gordian knot cutting that Mass Effect 3 did regarding previous game world decisions. UGH.
Worse, if I recall ME3 had 8 choices or something like that, this game has 3 and 2 just impact the villain.
Edit: And ME3 is a ME, same gameplay, same art direction. Veilguard looks nothing like the others.
Something something, new public, something something profit