There are only 2 series I have ever attempted a 100% run and those are Elder Scrolls & Grand Theft Auto.
Coincidentally the first Elder Scrolls I played was Morrowind, the 3rd one in the series, and the first Grand Theft Auto I played was the 3rd one. There weren't achievements on PS2 for GTA3 like there was for Morrowind on XboX, but there was still a % completion rate in the menu like all other GTA games.
For GTA3 it was the first time I experienced an open world as a criminal LOL, and that really pulled me in as a kid. That made me want to explore every inch of that world since I have never experienced anything like it before. For Morrowind it was the first time an open world provided no restrictions, you could literally do whatever you wanted to do. On top of that all the classes, socio-economic and Geo-political issues, and a ground breaking RPG structure, I was hooked. I remember just going to caves, ruins, camps, shrines, and forests all before ever doing the first main quest.
Ever since those introductions to the series I have 100% completed every game so far in each series.
However regarding every other game I play I would never dare attempt such a bold feat. I really dont think there is enough time in the day LOL. Too many games and too little time LOL.