Dark Souls. I just didn't get it at first. I struggled for like 40 hours grinding low level mobs thinking that buffing up my character will make the game easier, but I never got farther than Undead Parish and Darkroot Garden. I basically saw only a fraction of what the game had to offer and beaten maybe like 3-4 major bosses before I just got fed up with it and gave up, thinking that everyone must be suffering from some form of mass delusion for praising that game so much and being so elitist about it (which pissed me off to no end).
Then, a few years later, I begrudgingly tried Dark Souls 2, and it turned out to have a much lower barrier of entry and smoother difficulty curve, so with that game the combat of the Souls games finally clicked with me. But since level design in Dark Souls 2 was kinda shit and everyone said that the first game was much better in that regard, I went back to play Dark Souls 1 again, and that's when I fell in love with it. I was completely in the zone with that game, beating the whole thing in less than a week. And I loved every minute of it, even some of the more half-assed areas towards the end of the game.
Something similar happened years earlier with The Witcher, the first game. I remember absolutely hating it at first because it was long, obtuse, and the combat sucked. I didn't care about the Witcher lore either so I was bored with the story too. But then I read the books, got hooked on the story and characters, and then went back to play the game again and ended up absolutely loving it, along with The Wticher 2 which was also out by that time. I managed to do all of that just before The Witcher 3 came out so I was already so deep into it that I was just completely enthralled with the third game when it came out, and I remember spending the majority of that year playing nothing but that game and its first expansion.