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.
FEAR 1 and Wolfenstein TNO were some of my favorite games of all time so it’s only natural their sequels fell short.
In FEAR 2’s case, while it’s a rock solid shooter in its own right, it’s so obvious just how much it was trying to fit in the mold of the “gritty modern military shooter” that was predominant at the time (especially MW2). Stripping the tactical shooter elements like leaning still irks me.
For Wolfenstein 2, they tried to shake up the gameplay formula of TNO/TOB but the end result was something I was never quite satisfied with. To list some issues, Stealth went from being hilariously too easy to being a convoluted mechanic that I rarely ever used after the first engagement. Them splitting the Assault Rifle of the first game into the SMG and StG took away the entire point of the AR being a reliable weapon that was competent in most situations and replaced it with a useless peashooter (on higher difficulties) and cheesable death cannon respectively.