The Knight of the Old Republic games.
Reason: There are so many different paths you can walk, so many different ways to play the game, itès really fun to try them all out.
Morrowind.
Reason: It is an absolutely massive game that takes hundreds and hundres of hours to do absolutely everything in.
Chrono Trigger
Reason: Multiple endings make it fun to play through over and over to try and see them all.