The biggest difference between the Eastern and Western Fronts during World War I was that the Allied Powers (Britain, France, United States, Italy) eventually won the war in the west, whereas in the east, the Central Powers (Germany, Austria-Hungary and the Ottoman Empire) forced Russia, racked by revolution, to surrender with the Treaty of Brest-Litovsk in March of 1918, essentially ending the war on the Eastern Front. In fact, the Germans hastened Russia's surrender by releasing the exiled Bolshevik leader, Lenin, and several of his followers in April 1917. Within the year, the Bolsheviks had seized power in Russia and taken the Russian state out of the war. In the west, the inclusion of United States forces in 1918 brought the war to a conclusion with Germany's surrender in November 1918.
Another significant difference was that the two fronts were much different in size. While officially over 400 miles from the Swiss border to the North Sea, the Western Front mostly consisted of a series of trenches along the borders of France, Belgium, and Germany. For four years, the British, French and Germans dug themselves in and traded the same land back and forth in a brutal war of attrition that caused millions of casualties on both sides.
In contrast, the war on the Eastern Front spanned some 900 miles from the Black Sea in the south to St. Petersburg in the north. Battles were fought across this long front with troops traveling great distances to engage the enemy. Like the Western Front, however, the war in the east descended into stalemate until chaos and political upheaval exploded in Russia. Starvation, lack of weapons, and poor leadership caused the Russian army to flee the front and allow the Bolsheviks to sue for peace.
Technologically, the fronts were also different. British, French, and German armies employed a series of new technical advancements during the war on the Western Front. Tanks, airplanes, flamethrowers, and a wide range of other assorted devices were employed for the task of killing. Newsreels shot footage of early tanks, which were little more than tread, metal, and gun. However, they struck fear in the hearts of infantry men. Airplanes soared over the trenches and sometimes engaged in pitched aerial battles. Aviators like the Red Baron and Eddie Rickenbacker became household names. Most threatening of all was the introduction of mustard gas by the Germans at the Battle of Ypres in 1917. Soon enough, the gas mask became standard issue for troops on the Western Front.
The Russians not only lacked modern equipment, their country's roads and railway systems were totally lacking in their ability to transport troops in a timely fashion. Even worse, some of the country's nearly twelve million troops went into battle without guns. They would then simply pick up the rifle of a fallen comrade. Because of their primitive equipment and infrastructure, the Russians could only throw wave after wave of men at the smaller German and Austro-Hungarian forces. At the Battle of Tannenberg early in the war, the Russians, who fielded a much larger army, could not effectively communicate. They even let important uncoded messages fall into the hands of the Germans, who killed over 50,000 Russians and took nearly 100,000 as prisoners.