... I haven't finished many of those.

My reasoning behind them is based on how multilayered the levels feel or how in depth they are designed around gameplay mechanics and game's engine or how many secrets/puzzles and meaningful backtracking there is to do, or how many multiple paths they offer and how cleverly interconnect the area/s feel.

I think it could be an acquired taste thing, im not sure its your thing but its worth a shot, i guess the best way to go about them is to try first the game that matches your preferred genre, so lets say if its horror then Resdient Evil, if its Stealth then Thief/Dishonored (depends on action or hardcore), if its RPG then Deus Ex.