More can be written, especially if I'm misinterpreting. I can see two interpretations of your question.

If you are interested in that specific book accept no substitutes (it's assigned reading or something), then you might like to read these. The critiques I've found so far tend to just briefly mention some issue without a lot of detail.

• This in which /u/sunagainstgold critiques Tuchman's general approach. I think the other replies in the discussion are interesting but off the topic of Tuchman; it's talking about in-depth professional investigation and changing foci.
• In "The Guns of August and new WWI historiography" , /u/Gimpalong addresses "war by timetable".
• In "What do historians think of the book The Guns of August by Barbara Tuchman?" , /u/Bodark43 mentions British officers and the Balkans.
• In "How accurate is Barbara Tuchman's portrayal of WWI military leaders, particularly the field marshals?" , DuxBelisarius discusses exactly what's on the tin.

If your question is more "I want to learn about the start of World War I; is The Guns of August still a good starting place?", then you might like the AskHistorians World War I book list . I've now lost the link to the reply where someone suggested The Marne: 1914 over The Guns of August for the West. I can look for more book-list replies (I believe I omitted at least two for brevity).

This is not to discourage discussion. More questions, data, and debate are welcome.