Do you mean does it accurately portray the battle, or political realities? In both regards I think Solzhenitsyn does a decent job, and although he certainly has his outspoken opinions on the Bolshevik Revolution and Russian history, his characters in August 1914 are not simply mouthpieces.

As for his portrayal of the battle; I believe it is excellent. In particular his portrayal of General Samsanov is realistic , gripping, and remarkably sympathetic. He also gets the English General Knox to a tee. The battle scenes are not only wonderfully done but I think portray what it would have looked and felt like on the ground. He traces in painful detail the mistakes that led to disaster at Tannenberg.

That being said, as I mentioned Solzhenitsyn was a writer with very firm beliefs and has been accused of anti-Semitism, Tsarist apologia, and ultra-Orthodoxy. I don't remember it being too evident in August 1914, and here he is quite critical of the Tsarist regime. This also may depend on which version you're reading - the first version translated in the West was a shortened manuscript, while later a larger one came out adds hundreds of pages dealing with Lenin and the murder of Stolypin. I have only read the shorter edition.

All in all, I would call August 1914 a flawed masterpiece. I know some readers find Solzhenitsyn's prose turgid and perhaps a little inclined to rant, and with less effect than Tolstoy or Grossman. Still, when August shines it is a gem. Certain passages have stuck with me long after I read it.

I haven't read the other two books, although I mean to soon.