I think it was Grace Paley who said something like, "A story needs two stories. Not plot and subplot, but two stories that relate to each other."
When I'm planning something to write, I refer to these two stories as the Acute Issue and the Chronic Issue. Acute Issues are, well, acute: "Don't get eaten;" "Kill the monster;" "Stop the bomb before it hits zero." And Chronic Issues are more internal and long-lasting: "Stop feeling guilty;" "Find someone to love;" "Admit your mistakes."
I believe both issues are essential to a really good story. I think this is why everyone universally agrees that Terminator 2 is a better movie than its predecessor. Both had the same great Acute Issue: "Don't get blown to bits." But it's in the Chronic Issue where they really diverge.
Terminator has a love story as the Chronic Issue: it's fine and all, but we've seen it before. But T2 had a boy looking for a father figure he could trust. A great Chronic Issue, which was really well-developed in the script. And even though T2 is a thriller, even though its Acute Issue is what drew you into the theater, you just can't help but respond to the power of that Chronic Issue. And that makes T2 the winner hands down.
When you read thrillers that fail to include a good Chronic Issue, or literary novels that fail to include a good Acute Issue, you notice the lack. You may not know exactly what is missing, the way I wouldn't be able to tell you what's missing in mediocre music--but you know it's something.