The improvements include:

Reworking of the Zimmerman Telegram so that the timing of the decision to send it is dependent on the US mobilization level, thus making sending it far more useful for Germany.
Increasing the functionality of the swap move to enable more flexibility when moving units around a crowded battlefield.
Fixing various bugs, including one that slowed map scrolling.
Amending the way in which minor countries like Belgium and Serbia may continue in the war after their last capital has been captured.
- Increasing the impact of unrestricted naval warfare against the UK; the potential of the Arab Revolt, and the opportunities for operations in the Caucasus.
Germany will now have to keep some units in the east after Russia has pulled out of the war if it is to continue to receive grain supplies from the Ukraine.
- Significant work has been done to improve the balance on the Western Front in the 1917 Fate of Nations campaign.
Plus much more to make this game even more enjoyable.