Dragon Age Origins runs on relatively weak hardware (it's from 2009), epic story, epic characters, typically lasts around 40 hours if you do some of the side quests and talk to people.
Dark Souls 2 will run on a potato (A GT 640 holds ultra settings), looks very nice from an artistic standpoint, lasts ~80 hours or so. I love the minimalist approach, but you should be aware it doesn't have much of a story in the typical sense. It's more like Shadow of the Colossus or Ico in that regard.
Enslaved Odyssey To The West also runs on weak hardware and looks nice. Also a good story and good characters. I like the gameplay. It is kind short though, it took me ~10 hours to beat on normal difficulty. But, as a positive, when you finish the game once you get to keep your upgrades starting a new game.
If your PC can't run those even on low settings, then idk... That's getting into 8-bit or really old games as options.
There's still Morrowind (Steam). Or Red Faction 1 (Steam). Or Project Eden (GOG). Those are good games that'll run on literally anything at good settings now, being from 2002-ish. Games typically didn't have very well developed stories in 2002 though...