For me:

• Breath of the Wild: 400 hours in, have done only 50% of the game. But now that TotK is out, I'm not sure if I'll ever complete BotW. Perhaps if I'm stuck on a deserted island with my Switch and have nothing better to do, I may pick it up again.

• Skyrim: Countless hours, never really done much of the main storyline, always get lost in modding and optimising the game. Own it on practically all platforms too. But one of these days, I'll get to the main quest...

• Dangerous Dave: Been playing this DOS game on and off since 1990 but still haven't managed to beat it. I always die around level 6/7, blasted sun keeps killing me.