It's ~1,000 pages long, so I picked and chose which chapters I read. It's incredibly dense, but if you want to get deep in the weeds on the philosophy underpinning the Enlightenment, this book, and the other two in the series, will do it in spades. Tons of information and insight into how these men, some famous and some you'll only encounter in great detail in this book, really thought about politics, morality, and one another.
Two warnings: First, a passing familiarity with French and German and Dutch will make things easier, as the author intersperses phrases from the original thinkers' works into the text. It's great for about 100 pages and then you realize many times he's leaving key parts of the sentences in a language you may not be able to read, or may not be familiar enough with the language to grasp the translation. At that point, it's aggravating and you have the sneaking suspicion you're missing interesting points.
Second, the guy's sentences are very long. Too long, really and he should have had a better editor with the guts to tell the guy (he's a scholar at IAS at Princeton...so probably not used to being told to be more succinct) to take 1,000 pages and make it 500 and call it an opus. On multiple occasions, an entire paragraph was a single sentence linked together by commas and semicolons in a Frankenstein's monster of a sentence. By the time you get to the end, you've forgotten what point he was trying to make. Again, aggravating. How an editor let that pass is beyond me.
Bottom line: this book is chock-a-block full of information about the Enlightenment and if this is something you've always wanted to explore inside and out, then read all 3,000 pages of this series. If not, it's still worth skimming the chapters you're most interested in, and leaving the rest for posterity. But be warned that the author writes firmly in the humanities tradition of "why say something with 10 words, when 30 will make it sound smarter." You'll be as purple as the prose if you try to digest the entire tome.