I think Kurt Vonnegut’s The Sirens of Titan is the most old-school science fictional of his books I’ve read. It’s kind of like Stranger in a Strange Land, with its messianic outerspace weirdo, though in Sirens of Titan he was a human space explorer who got caught in an anomaly that spread him out and made him much less situated in space and time. He also starts a war between Mars and Earth for a very convoluted reason. The entire thing is convoluted really (though I figured out how they could escape the labyrinthine tunnels of Mercury long before the characters did).
It’s about luck and the way things seem to work out. And about the stupidity of the military. And war and religion. And the point of all human existence is revealed in the book, so that’s something.