Storyline is important in RPG, but I like when you can pick alternative ways on completing quest, either you can do it in a good way, or a bad way or with persuasion.
Meaning, on action you pick, will determine the next story line. Later you character will be lawful good, chaotic evil, or just natural.
Example, Fable or Starwars: KOTOR.
This give more depth when you play the game second round or with second char.
Ending is the important thing, you been playing for +300 hours, the reward should be satisfied, at least the last boss battle should be epic.
Speaking of last boss battle, TL should have uber power optional boss as well, to reward their great loyal fans ( pointing to Fhaarkas

)
FF have it, Borderland have it.. and the reward should be like alternate ending video, new game+ with new character new story line, really hard to get gear or something.