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.
HOT TAKE: Star Fox Zero is the best entry in the franchise since 64. It delivered on every single thing the fans of SF64 wanted but because it got bundled with a controller gimmick that's all anyone could talk about, even though every other game that has motion aiming gets praised to high heaven because it's objectively a better way to aim a gun than a second thumb stick.
It was hard for me to experience the better gameplay you're talking about because the controller gimmick was mandatory and very unfun for me to play with. I wasn't particularly fond of other games using that second screen as a mandatory inclusion, either. Also, because it's a story rehash, it felt more like a pretty but clumsy SF64 remaster than a new game.
The opening cinematic was amazing and should have been its own movie/show, though.
I mean it's all subjective but I personally liked the controls and I'm sad about how hard they were rejected by the masses I do dream of a Switch port that makes them optional though, because I feel like the game itself deserves a second shot. There's a lot to like in the campaign (except for that helicopter level).
I don't want to yuck your yum there, so I'll just share frustration that Star Fox is probably mothballed indefinitely now.