When I was a kid, my brother and I could never get past the first few levels of MediEvil for the original Playstation. The game used to scare the piss out of us, though looking back now it was extremely cartoony and not that bad at all.
Years later, we played through the whole game and got every chalice. God that felt amazing.
Back in the day if I found an RPG I really liked, I'd play through it countless times, so I'd have a run where I'd grind real hard, real early and get to ridiculous levels and just blast through the game, another time I'd avoid grinding as much as possible and try to make my way through the game at ridiculously low levels, I'd try to beat the game within a certain period of time, all these sorts of things.
I comprehended a SaGa game (Romancing SaGa 2) enough to not only finish it, but beat all the optional bosses as well. Might not seem like much, but those games have always seemed impenetrable to me.