Fallout really didn't have a storyline, but it was one of my favorite action-RPGs of all time. Mass Effect has the best storyline hands down.
Anyway, I can recommend three games:
Dragon Age:Origins (probably my favorite all time RPG for its overall elements) very long playthrough. If you get the Ultimate Edition, it has all of the DLCs and the Awakening expansion, making this game a seriously long play-through (I'd say 150 hours for the Ultimate edition). The storyline is rich with many companions in which you can interact with in many ways, aside from your main character.
Elder Scrolls IV: Oblivion - gorgeous game, some bugs, but a huge world and lots of quests. GOTY edition is very cheap and very long to play through.
The Witcher. My least favorite, but you can get this game very cheap and the story is good with nice environments and a good storyline. Nice combat system.