In terms of photography, yes film grain and low depth of field are the most common elements. The vast majority of these photos are shot on film which gives them the pleasant "graininess" and a particular sense of color. Depth of field has to do with the aperture of the camera so that only things in a certain distance are in focus and other things are tastefully "blurred." That's about as technical as I can get with photography specifics.
In terms of composition and subject matter, I definitely tend to prefer images that have a feeling of contented solitude. Most of the ones I post don't have people in them, or if they do, the people are kind of anonymous or secondary to the scenery. They're props more than subjects. And I tend to prefer more every-day kind of imagery vs sweeping vistas or skylines shot from the air or something. The kind of thing you see every day. Or at least would see every day if you lived near where the photo was taken.
Mostly I just collect images that to me immediately invoke some mood or feeling. Where just by looking at the image you can tell what it would smell like there and almost feel the cool crisp air on your skin. I've seen people describe it as a sort of nostalgia for something you've never actually experienced. I think there's some accuracy to that.