The introduction to this edition is by Ursula Le Guin. Here is part of her description of the book:
Roadside Picnic is a first contact story with a difference. Aliens have visited the Earth and gone away again, leaving behind them several landing areas (now called the Zones) littered with their refuse. The picnickers have gone; the pack rats, wary but curious, approach the crumpled bits of cellophane, the glittering pull tabs from beer cans, and try to carry them home to their holes.
Most of the mystifying debris is extremely dangerous. Some proves useful — eternal batteries that power automobiles — but the scientists never know if they are using the devices for their proper purposes or employing (as it were) Geiger counters as hand axes and electronic components as nose rings.
In the traditional first contact story, communication is achieved by courageous and dedicated spacemen, and thereafter ensues an exchange of knowledge, a military triumph, or a big business deal. Here, the visitors from space, if they noticed our existence at all, were evidently uninterested in communication; perhaps to them we were savages, or perhaps pack rats. There was no communication; there can be no understanding.
I doubt I’m the only one who thought of Peter Watts’s Blindsight when I read that description (the last paragraph above). (Or the other way around, as Blindsight came out in 2006). I really liked the set-up, so this book drew me in at the beginning, but somewhere around the halfway point the characters and dialogue started to seem a bit perfunctory, and if it hadn’t been so short I might not have bothered to finish it, but I was curious. The ending is disturbing, but I think it would have had more impact if I had been more invested in the story earlier on.