Timelike Infinity is the second in the Xeelee sequence, but pleasingly does not rely on knowlege of its predecessor - Raft. Sharing neither characters or setting, (it is in fact set millions of years prior to Raft - and in another universe!), Timelike Infinity instead concentrates on its own era of humanity, but contains a few teasing morsels that enrich the background of Raft.
The story itself concentrates on time travel, with pleasing dashed expectations all round; a human travels to the future expecting to find progress and instead finds humanity under the yoke of the alien Qax; from this future one of the Qax contacts his descendents even further into the future expecting information on how humanities subjugation was held - instead learning that the Qax are themselves to be overthrown. Added to this is a host of hard-sf musings on quantum physics, the nature of time, and black holes. There's altogether less invention and excitement than in Raft, but here the characters are more likeable and well-rounded, with even some time for some humorous interaction between a life extended human and a physically younger AI of his father. Theres a pleasant, if slightly ambiguous ending, but the standalone aspect is slightly scuppered by a final paragraph that seems to have no meaning within the context of the novel itself (a trailer for Flux perhaps).
Recommended for the quality of ideas, just be prepared for entertainment of a more cerebral sort than the sense-of-wonder world-building of Raft.