Both Baldur's Gates: With the huge amounts of sidequests (some depending on who joins you), character interaction, people that can join your party, etc. I wouldn't be surprised if you need three or more playthroughs to see it all. Avadon 1 & 2, albeit to a lesser degree: You have different mutually exclusive storylines and endings. Also, very good games in my opinion. Banner Saga: lots of choices, reminds of King of Dragon Pass. King of Dragon Pass: not a true RPG in the strict sense, BUT: this is THE best game out there if you really want to play a role and immerse into it. A chieftain of a Celtic-inspired tribe, in this case. Shadowrun: Both games, I guess. I only played the first one so far, and you pretty much get the same stuff as for the others above: quite a different experience depending on your choices and character. Heroes of Steel: more of the above replayability.
^very good list... Adding these: Pen &Paper RPG Star Wars KOTOR Battleheart Battleheart Legacy Wayward Souls Crystal Siege Heroes & Castles Monster Hunter Freedom Unite (has lesser RPG mechanics than those above, but is easily has better replayability)
