Half-Life. I went through this horrid phase that lasted around nine years where I would tell myself NEVER to play an FPS game, because of how bloody and gore-ish some of 'em can get, and due to some other factors that I will not get into here.
A couple years ago, I bought GMod to play around with the physics engine, and then bought HL2, and then HL2, in typical me fashion, beating the sequel / remaster before the original.
Half-Life and its sequel were amazing. I enjoyed every last second of both of them, and I nearly completed "BLACK MESA" (Half-Life's fan remake) before the original lmao
Another game that I believed was horrible before I got into it was "UNDERTALE", simply due to the "Should be burning in Hell" part LOL
And then in 2019, I played it for the first time, got through the Pacifist route in six and a half hours, and cried like a baby during the "New Home" segment where the main game overture played. To this day, I still haven't got the will to kill everything lol.