Something Coming Through by Paul McAuley. Summary: meh. Read again? No.
Recommendation: 400 billion stars is his best work. It is hard to produce two like that; and he hasn't. Read that instead. The Quiet War stuff was also almost good; better than this, but didn't live up to its promise. Unlike 400 billion stars, which massively over-delivers.
Spoiler alert: don't read on unless you're not going to read the book.
The premise is a damaged Earth where aliens have turned up and "helped" by giving access to distant worlds, but left us largely alone. On those distant worlds - one in particular is the subject of the book - remnants of multiple alien cultures have been found, former clients of the aforesaid aliens; and some remnant artifacts - eidolons - have the capacity to "haunt" people, or act like brain viruses.
It's not a bad premise and could have lead to a decent book. Sadly, it leads to a detective story which could largely be mapped onto any genre and thus largely lacks interest. All too typically, past the first idea the author really has nothing in reserve for the ending: pretty well nothing happens except some more inexplicable starships turn up.
Sociologically, perhaps the most interesting part is the way that humanity, transplanted to a new world, largely ignores that world and instead falls back on all its old corruption and vices. That could have been interesting. But since it mostly gets in the way of the ostensible story, it isn't. Better would have been some contrast between those who do explore the new world (there should have been people trying to piece together all the dead cultures) and those who turn their back.
Speaking of the dead cultures that are found on the other worlds, there is remarkably little interest about them in the book. But imagine it: you're gifted a pile of worlds where other cultures, also gifted with those worlds many years ago, died out. Everyone would be wondering "so, is it us next? Is there something dangerous about these places, is this a poisoned gift?" But not the people in the book.
Real science error: one of the things in the book is an alien ray gun. In the beginning it is mysterious, a rumoured possession of a criminal. Eventually it is "explained": it is a "ray gun", it converts with near 100% efficiency the power of a battery cell into (effectively) laser light. But, but: that's not good enough. There isn't enough power in the cell to have the effects described, even at 100% efficiency. Also, such a device would be massively valuable; the criminals of the story, instead of spending so much effort on unclear archaeological explorations (which they cannot have known would pay off, though the book treats them as so determined that they appear certain; another plot hole), would just have sold it.