I read Roadside Picnic a few months ago, and yeah, it's very good stuff. While there's a lot to be said for the context in which it was written, I think it also holds up on its own even if you're not very familiar with the history.
Roadside picnic is so ridiculously melancholy. Everyone in that book is so depressed! I also don't think I've ever seen so much smoking and drinking in a sci-fi book. You could tell the brothers were really not enjoying communism.
The novel itself and the setting are not about communism though, not even in disguise. It would have to be in disguise because the setting is an unnamed North American (possibly Canadian?) city, but even if it was, the themes are not about communism.