From: Vancouver, BC
It is quite a different game from the WW2 game. The Central Powers are divided between three Majors: Germany, which is the strongest power but nowhere near as dominant as it is in WW2; Austria-Hungary, which is much stronger than Italy in WW2 as the number two ally; and the Ottomans, who are weak at the start but can grow significantly if not attacked and which occupy a lot of strategic terrain. The Entente is also a more plural side, with Britain and France roughly co-equal powers with different strengths and Russia, which is the weak sister of that alliance, and which is ultimately undermined by revolution within. Italy and Serbia also can prove surprisingly resistant thorns in the side of the Central Powers. The U.S.A. does usually enter the war, but when depends a great deal on German submarine strategy against Britain. Artillery is the key technology, in place of aviation and tanks (though tanks do make their appearance later in the game and there are lots of planes which primarily make your artillery more effective through spotting). The German navy, though still weaker than the British one, is much larger than in WW2 and can challenge Britain if skillfully used. Spotting and Fog of War are a bigger factor in the WW1 game, because aviation is much weaker and trenches block sight lines, so using airships to know what is going on beyond the enemy front line is important. The pace of combat differs more from front to front - not surprisingly, you have slow, grinding attrition on the Western front and the Italian and Serbian fronts, but more open campaigns of movement on the Eastern front against Russia and potentially in Mesopotamia and Palestine against the Ottomans. But because cavalry is relatively weak, you rarely have the kind of breakthroughs that tanks in WW2 can achieve. More Minor powers survive the opening year of the war, especially if Germany decides against invading Belgium, and they offer more strategic options if you can use diplomacy to recruit one or two to your side. But none are as strong as Spain or Turkey in the WW2 game. Perhaps the biggest difference is that National Morale is the key strategic factor in the game: every Major can be defeated by having its NM driven to zero and by 1917-8 every Major is battling on with NM factors that can be below 50% - so capturing territory and destroying units to reduce National Morale plus the reciprocal naval blockades by Germany and Britain are essential strategies.
Overall, for the modest cost, it is worth buying and deciding for yourself.