Guns of August was awesome... Facts SUPPORTED by evidence, btw.
Yeah, "facts".
And I'm not going to be an asshat about this because I was there about 2-3ish years ago.
The Guns of August, while being an excellently written piece of history (as all of Tuchman's books are), it is not really a book you should be citing as a history of the First World War. To start with it is over 40 years old. That's a major red flag, especially on histories of the First World War, where anything written before the fall of the Berlin Wall (and subsequent freeing of Imperial Russian and German records to Western study) is highly suspect and an incomplete picture to be sure. Second the book is written by a nonacademic. While that isn't automatically a strike against a writer, it means they aren't necessarily engaged in the same sort of academic dialogues, rigor, and scrutiny that an academic at a university would undergo.
The sources Tuchman uses are very dated and very biased. Her opinions on the so-called Schlieffen plan largely come from Liddel-Hart, who himself was quoting from post-WWI accounts by German officers (notably the German railmaster [his name escapes me at the moment]) who were mostly trying to absolve themselves of blame for the disastrous events of WWI, particularly its opening months and the seeming unforced bungling of the Marne. Because Helmuth von Moltke the Younger was dead, he made for a very easy scapegoat for these officers, and it was relatively easy to bring up Schlieffen (a well-regarded Chief of the General Staff) and his plan as a counterpoint.
In addition Tuchman is a deep Anglophile and even deeper Germanophobe. She lets this affect her characterization of German plans and operations, falling slightly into a modified
Sonderweg (From what I remember, although Dachs is free to tell me I'm completely wrong on this) argument, characterizing the German military staff as warlike, hawkish, and brutally efficient. She never really looks into the serious problems facing the British government at the time, and how those problems affected British international policy. The way she characterizes things you get the sense that Foch and French basically had total control of French and British war planning.
The big problem is that she totally overstates the influence Wilhelm had in German policymaking. This ties in with her Germanophobia. She characterizes Wilhelm as a baby-idiot-savant unsure of what he actually wants, and essentially blames the whole war on him. In reality Wilhelm really didn't have a lot of control on German government or policymaking. He had control of appointments, and his influence in the German Admiralty was certainly substantial, but to call him an absolute monarch (which is essentially how Tuchman characterizes him) is ludicrous. She also does this with King Albert I of Belgium on the opposite end of the spectrum (from the way she describes him you'd think he fought off the German advances all by himself).
Finally there's the obvious Elephant in the room: she completely ignores: The North Sea, the colonies, the Eastern Front, The Ottoman Empire, and pretty much everything except for the Marne campaign.
If you want a truly good basic overview of the first 1.5-2 years of the war, the classic is Huw Strachan's
The First World War, part I: To Arms!. It really is the gold standard as far as a comprehensive history of the First World War goes. Also I would recommend
Dachs' history article on the historiography of the Schlieffen Plan for a more thorough explanation of what it is, why it's mischaracterized, and how scholarship on it has dramatically changed in the last 25 years or so.