Just bought August 1914, by Solzenitsn, which I probably can't spell right. Haven't started.
Let me know how it is. Tannenberg is a highly underappreciated battle. The Germans won, of course, but in the meantime they old Prussian Elite had become nervous due to the Russian hordes invading their homeland. That nervousness probably ended up costing Germany their best (and probably only) chance to win WWI. Short version:
When the Prussian Elites raised alarm over the Russian invasion of East Prussia the issue became such that the Imperial General Staff had to respond. Their response was to transfer an entire army from the Western Front to the Eastern Front to meet the threat.
Unfortunately for the Germans, this transferred Army was in transit (W->E) when the decisive actions against the Russians occurred in East Prussia and again in transit (E->W) when the Battle of the Marne stopped the German advance into France on the Marne river.
Notably, the German army that was withdrawn from the Western Front due to the apparent threat in the East was taken from the exact spot where the French discovered and attacked a large gap in the German line. Had it not been for the Russian invasion of East Prussia these troops would never have been taken off of the Western Front and it is entirely possible that France would have been knocked out of WWI. Given that Tsarist Russia subsequently collapsed it is entirely possible that this could have dramatically altered the outcome of WWI.
Barbara Tuchman's Guns of August is a great read about the diplomatic attempts to avoid the war and the early days of WWI.
WWI is fascinating to me, moreso than WWII. The technological changes during WWI were, IMHO, even more immense than during WWII. Look at aircraft, for example. In the fall of 1914 when the war started the aircraft mostly looked pretty much like the Wright Brother's original flying machine. They were mostly wood and cloth bi-planes with almost no armor or armament. By the fall of 1918 there were some very modern-looking all metal monoplanes with substantial armor and armament. Similarly, on the ground at the beginning of the war Cavalry was a major weapon and rifles were similar to the ones used by the armies of Napoleon and his enemies a century earlier. By the end of the war there were tanks and machine guns.
The cultural changes brought on by WWI were also immense. At the beginning troops in Austria Hungry answered to an Emperor, troops in Russia answered to a Tsar, troops in Germany answered to a Kaiser. The families of the Emperor, Tsar, and Kaiser had ruled at least parts of their respective lands for centuries. When the dust settled after WWI the Tsar and his family were all dead and Russia was ruled by a Politburo. The Austro-Hungarian Emperor died during the war (he was over 80 when it started) and at the end of the war the empire was dissolved into many pieces and his successor lived out his post-war life in Madeira in exile. The Kaiser fled Germany at the end of the war and lived out his days as an exile in the Netherlands.