Terraria. I have so many playthroughs still unfinished.
My master mode playthrough is still unfinished, my Calamity mod playthrough is still unfinished, and my Spirit mod playthrough is still unfinished. I pretty much got distracted a lot and ended up playing these three different playthroughs at the same time. It's honestly fun, but it's making the playthroughs longer than usual.
It has been a year and I haven't finished them, I'm not kidding.
Not to mention, I am also obsessed with playing Stardew Valley.
The fishing in Stardew Valley is so addictive that I still haven't finished my first playthrough of the game. And with the updates being released as I played the game, it got longer and longer. I am literally in my third year in-game, and I'm still like less than an eighth in terms of game progress.
I had to literally stop playing for half a year, because I was obsessed with fishing everyday in the game.