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.
That's the one with the worst optimization. 3 kingdoms, warhammer2 troy all have higher fps in my PC, granted I'm running a potato, but still. Attila is the total war game with worse optimization. Other than that it's just a reskin of Rome 2 wich is garbage.
Rome 2 was garbage, but it is no mere reskin! have at thee!
All games after Rome 2 are a reskin of Rome 2. If Rome 2 was a reskin of shogun 2, that would be very cool.