Pandora's Star by Peter F. Hamilton
I got this book under the assumption that it could be read as an independent novel, although it is part of the Commonwealth series. It turned out that it began without giving me a problem understanding what was happening, but it did not end with a conclusion. Therefore, I can't recommend this book as a separate book - and I haven't read the whole series. The sequel to this book is Judas Unchained.
The central premise is that humans have spread to many other star systems. These worlds are linked into a commonwealth via wormhole transportation and communications. Two stars about 1000 light years from human areas are observed to "disappear". Further investigation shows that the two star systems have actually just been enclosed in vast forcefields that only let out some infrared radiation. Nothing else can go in or out of the star systems. Humans conclude there are two possible explanations -- some very advanced civilization has either enclosed their own star system to protect themselves from some great threat or a very advanced civilization has imprisoned some dangerous civilization inside that species' star system. In either case, there is a very advanced civilization and possibly some serious threat in the galaxy.
An expedition is sent to learn more about the two star systems. While the expedition is studying the forcefield, the forcefield mysteriously shuts down. The civilization in that system has colonized all the planets and other substantial bodies. When the local civilization realizes the forcefield is gone, many spaceships quickly head out of the system. When the human ship is detected, some spaceships go to intercept it. Some of those ships fire nuclear missiles at each other and at the human ship. Generally, the locals start warring with each other, making them look warlike and dangerous. The human ship is not prepared to take on a fleet of alien warships. They decide they must leave quickly even though that means leaving 2 crew members who didn't return in time from investigating an old alien artifact.
The book is like a mystery with a number of subplots that have puzzling elements. The subplots are not clearly linked at least for an extended portion of the book. The subplots include: a secret group dedicated to the cause of opposing what they claim are the schemes of an alien from a crash-landed spaceship, a police detective working on various crimes (including arms smuggling by a terrorist and an old double murder of a pair of lovers), a bohemian old techie who was one of the inventors of wormhole travel, a species of aliens who behave like playful youths and speak in cryptic / poetic ways (and has some advanced technology "indistinguishable from magic"), the people involved in building and crewing the exploratory starship to the enclosed star systems, a view of the species and society of the civilization at the enclosed star, and some of the aristocratic mover and shakers in the human interstellar society.
Although there aren't any absolutely never-before-seen ideas coming out today, the book's material is as reasonably fresh as one might hope for.
Generally, Hamilton expands scenes far beyond what is needed. Most writers will describe 30 minutes or an hour to include a significant 5 minute event. Hamilton will describe an entire day to give you that significant 5 minutes. For example, we have a scene focused around a character supervising the exploration of a new planet via wormhole. The initial surveillance by machine and then deployment of a team of explorers is described in detail. But at the end of the scene, the only essential fact is the character is talked into leaving this job to take on a different project. There were a number of reasons why a reader might find the investigation of that new planet interesting - it's just not relevant to the rest of the novel. Perhaps Hamilton could find some other way to give us these interesting bits and pieces. Maybe they should be developed into separate short stories. Maybe they could be packaged as little stories in something like an appendix at the end of the novel - sort of like how they sometimes include scenes cut out of a movie at the end of a DVD. As far as my own inclinations are concerned, I found the story of Pandora's Star complex enough without adding these dead-end side passages as well. As one can see from the list of subplots, the story would not be left thin or dull by the absence of these random pieces. And they also contribute to making Pandora's Star a rather long book.
By itself, Pandora's Star is 800 pages long. If you add the length of the books before and after it in the series, it could be a major reading project.