My gut reaction about lit vs genre fi used to be "Well, sure they're different," but then I when I try to formulate exactly what those differences are, I haven't been able to do it. For any feature (e.g., "simple plot structure") that I think characterizes the one, I could just as easily come up with a title that's obviously in the other category but that shares that feature.

The only thing that seemed like it might work was reading level. Lit fi seems to be written at a higher reading level than genre fiction. Again, there are exceptions (e.g. Hemingway), but in general they seem to be less demanding texts to read.

Maybe genre fiction is like pornography: "I can't define it but I know it when I see it" ?