Similar enough you can begin play right away.
The biggest difference for me was the change in command and control. You now have a supreme commander who creates army commanders. Two for Germany, one for all of the other major factions. Their proximity to active fronts are important to managing your armies.
The naval war will feel familiar in many ways, but with more detailed blockade.
The Entente is two factions, which matters most in pbem play, but creates some differences in resource allocation, also.
A really nice plus is the use of warplans as the game opens. You can experiment with different initial deployments as you attempt to win the war quickly.
Diplomacy: In this game, some minor powers might join either side depending upon how you play diplomacy. If you are familiar with the war, it tends to follow similar patterns, but your play might shape actual factions engaging; like for instance the entry of Italy.
Probably the major difference in play is you will soon have continuous fronts in the west and maybe in the east, so maneuver after the opening moves is on a grand strategy scale. Also, the clock is always ticking on the outbreak of the Russian Revolution.
If you did not yet purchase it, the Breaking the Deadlock expansion is well worth buying as it provides many small regional conflicts allowing for study of other theaters of war.