Literature vs popular fiction

One is considered "high art", and the other part of lowly "popular culture", but what is the difference in content?

The "think and feel" approach seems to be the most logical. Most classics are very simple stories that don't show as much creativity or magic as popular fiction. Frankenstein has a person being made out of corpses but the rest of the cast is awful plain except for Victor. But Harry Potter has a ton more fantasy to it with a larger cast of more interesting characters. So what's the difference? Frankenstein is supposed to make you think.

I'll throw in something else.  Not only does literature make you think, it makes you think about the world you live in.  Furthermore, it makes US think about the world the writers lived in; in effect, it acts as an artifact of the world it inhibits.  Harry Potter may have more interesting characters, but in the end, it's just another bildungsroman that reveals little to nothing about the world the author inhabits; what's more interesting about Harry Potter is that it was, for the target audience, a book you read because your friends read it, not because you really wanted to read it.

When Shelley wrote Frankenstein (or as the subtitle calls it, "The Modern Prometheus"), one of the big fears of the early 1800s was that Man was advancing in Industry and Science too quickly, stepping into the shoes of God, a theme that runs even to this day.  What makes the story so enduring is not, as the quoted poster said, the characters (only Victor and the creature are at all interesting), but the theme behind it.  It's not an original anxiety, but it's presented in a fairly original way that makes it more presentable to your average reader.