John Brunner is best known for his dystopia novels, usually set in an America headed for destruction. (Many people are surprised to discover that Brunner was British; he writes about the US from an insider's perspective, and has the rhythms spot on.) The most famous of these is The Sheep Look Up, which is not one of the books that I am reviewing. My point is that while Brunner often writes dystopias— and given the time period, such fiction is hardly surprising— he also writes books with a great deal of hope.
As an example, The Jagged Orbit is a classic dystopia setup, with a degrading and increasingly polarized society spurred to greater fears and isolation by weapons manufacturers who want a better market. And yet there is a hopeful tone present that is unlike such novels as The Sheep Look Up; Brunner lets you get close to the characters, and allows you to think they might succeed. As a minor spoiler, the do get that chance, because the reasons for the destructive pattern become evident to the point that they are able to turn them around, at least within the limited confines of the novel.
Interstellar Empire is also not particularly dystopic, though its stories are set in the slow collapse of a galactic Empire. Fans of Asimov and his Foundation series will recognize the feel, but these stories are more simply old-fashioned action SF. Quick and easy read.
Quicksand is a bit more depressing. It's not set in an obvious dystopia, but at a calm mental institution, where a strange young woman with seeming aphasia (the inability to understand language) is sent following an altercation. The physician in charge of her treatment becomes more and more obsessed with trying to find out her story as she gradually learns our language, and this affects his personal life deeply. However, the end to this novel must be read carefully as it is vicious and abrupt, and not at all what is expected. This is a good book but not something to read in a bad mood.