Okay, so the rundown is as follows*: Lexicon is not a great book, far from the best book of the year, but it's a solid read. The characters are fairly interesting, the darkly humorous tone carries the book a lot, and the pace keeps the reader moving even in the parts when the book flags. The bad bits come in with a mystery solved in cop-out, some confusing flashbacks that are not told in any conceivable order, and a surplus of plot elements that, while touched upon, are never fully discussed.
In the end, while it's a dynamite book on its own terms and when put up against most of the literary canon to date, it's a disappointment from the man who wrote Syrup, Company, Man Machine, and Jennifer Government. Get this one from the library, enjoy it in the three or four days it'll take to read it, and then move on to better things. It's enjoyable, but I wouldn't buy it. More, as always, below.