Thanks to a little stomach flu, I just managed to finish the war with a decisive victory for the Central Powers in January 1917 (normal difficulty). The AI is fine, though rather easily tricked by a little WW2-style blitzkrieg strategy and sometimes not aggressive enough (especially at sea). Here's a little first impression AAR.
Garrison units were key to quickly defeating Serbia and stalling Russia. Austria-Hungary deployed three new garrison units to the Serbian front on turn 2. I simply sent them through the undefended gaps in the Serbian line and the AI now has to choose between ignoring these units advancing on its cities or abandon their fixed defenses. And once entrenched these garrison units become very hard to dislodge for 1914-era infantry. This allowed me to isolate their cities with well-placed garrisons while 3 infantry units neutralized them one by one once I was able to build some artillery.
The Russian front was a simple trade-off of space for time, the reverse of what happened in WW2. Austrian forces held the Russian flank with three garrisons and an infantry unit, despite losing their border fortress. German forces allowed the Russian to slowly advance, building a thin, broken line between Danzig, Stettin and Breslau (Posen was quickly lost). Konigsberg managed to hold out for nearly two years while completely surrounded. The Eastern front remained pretty immobile until the end of 1915, when reinforcements arrived from France and Serbia.
The invasion of Belgium and France was a huge success. Brussels was taken on the second German turn, Calais was secured by an advance Cavalry unit on the turn afterwards. The High Seas Fleet managed to surprise the BEF transports, killing a British infantry unit and damaging another before withdrawing. Nearly all German reinforcements were poured into the Western Front, and Paris fell in the first weeks of 1915. The majority of the French army was enveloped by weaker but well-entrenched garrison units around Verdun and the French-German border. Once Northern France was secured and the main German forces turned southwards and eastwards, they were easily decimated. When Italy declared war in May, Marseille had just fallen. France sued for peace one week later. A few German units were turned towards Italy, while the rest hurried to reinforce the Russian Front.
The Ottomans had a hard time in the meanwhile. With the Western Front in tatters, the British sent nearly all of their troops to invade Palestine, with only a few units aiding the Italians. The Ottomans were pushed back to Damascus and Beirut and could barely hold.
Back in the East, the German and Austrian reinforcements were quickly pushing back the Russians, while the German Fleet annihilated their Battleship unit. By march 1916, the Russian revolution was in full effect and one more front fell silent. Austrian and Bulgarian units (who had just taken down Romania) were then sent to reinforce the Ottomans. Some German forces were diverted to a breakthrough in Italy. With Florence under siege, they also quickly surrendered.
The rest of the German Army was preparing for the big one: Sealion! With German air superiority over the Channel, London suffering daily zeppelin bombardment and the British Cruiser squadrons ambushed and destroyed by the High Seas Fleet, the first German troops crossed the Channel in the summer of 1916. I had to hurry, because the US was strongly complaining about my convoy raiding and would soon join the war. British resistance proved rather weak, after all of their losses so far and most of their army stuck in the Middle East. So on January 18th, with German forces on the outskirts of London and Leeds fallen, the British Empire formally surrendered.
Thus ended the Great War, and the world would never be the same again.