So I've finally finished reading the Xeelee Sequence books -- or at least the books of the main storyline. (I'm still missing Flux, which is basically a spinoff, and Xeelee: Vengeance and Xeelee: Redemption, set in an alternate timeline).
The web consensus appears to be that these books form the darkest, most horrifying setting in science fiction, WARHAMMER 40K on Bath SAlts!!1!! and there is much of that, but honestly they are not quite as nihilistic as the meme would have you believe. Yes, the setting is indeed full of brutality, oppression, death, and pointless suffering -- much like real history. They are still full of acts of kindness, help, and wonder. Most of the individual stories manage to end on a high note, even!
I was told that the aliens are so alien that no communication, cooperation, or quarter is possible, but humans and Silver Ghosts manage to coexist on the frontline for centuries, Jack Raoul and the Ghost ambassador are outright friends, and it seems that would have lasted much longer hadn't the human Coalition been so intentionally xenophobic. Even one of the Qax (the convection cell-based beings that enslave Earth for 400 years) gets along pretty well with a human underling, before being murdered by another Qax for being too soft on humans. A major theme of the whole series is that symbiosis and cooperation are extremely common and useful! And the Xeelee are downright benevolent when you are not actively shooting at them out of empty spite.
I mean, it's not a happy setting, not in the slightest. It's just not the endless horrorfest it's said to be. Usually.
Anyway, I'm going to celebrate these books the way I know best -- with an obsessively detailed infograph (spoilers!!):