Aldous Huxley wrote two versions of utopia: Brave New World early in his career, and an almost forgotten novel, Island, right at the end. The difference is that Island is not meant ironically. Huxley really believed that love, sex, reason and humility could make the world a kind of paradise, especially when glued together with hallucinogenic drugs.
Considered as a style of fiction, what distinguishes utopias is that they work best when they are least psychologically credible. This is also what distinguishes them from the greater part of science fiction. The incredibility that makes utopias valuable is of a particular sort. It’s not technological—by now there is nothing that seems technologically impossible to the contemporary imagination—but psychological: the idea of a state of permanent happiness and balance, where all dangers are properly controlled seems, literally, too good to be true. That is usually taken as a weakness. But that reaction is exactly what makes utopias valuable. Chasing down the intuition that something is too good to be true can show us something about both goodness and truth which we can’t see as clearly from any other perspective.