(hi-fivez)
To be honest, I don't really know if it's fair to leave out Mafia, PS:T, IWD2, Thief 1 and Undying, but TLJ, T2 and Rome are the ones I go back to play again and again, even if it's just for more mods. Those games have had incredible longevity for me, through mods or through plain story-galore. I hate leave the list like that, but no other games have just lasted with me for so long.