It seems like neither Inn nor even Piknic (which is a true masterpiece) is the their most profound work. I would suggest "Snail On a Slope" (which I have read at least 10 times) and especially "Ugly Swans" - these novels, it seems, has the brother's philosophy fully developed and refined.

The Roadside Piknic is the first enlightenment, so to speak, the bold conclusion that there is no way out, but selfless wish for happiness to everyone as the only way to hypothetically change the world (the way of the East - to focus on inner rather than social development, in hope that a proper social system will naturally follow, at least to some extent - the way of Gita or Spinoza, the way of India, and some Buddhist countries).