Well, even when you can evaluate a purchase if you want the discount you need join 5 titles that is a killer for impulse buy
In WWI are interesting battles-campaigns and with more to offer apart trenches blood and mud.
For example i allways find interesting the Meggido campaign because armies are small for the WWI standards and is a lot more mobile combat + some exotic flavour, being a small battle help create interesting what ifs and variants adding a few extra units (bigger Asia Corps and why not USA and France reinforcements).
Anyway in late 2019 or earlier 2020 a new title is going to arrive to FWW serie... part other titles in other series.
Kaiserschlacht is interesting to maybe like F14 but with more deadly but better protected units... closer to PzC but lacking armored divisions and an arty less flexible to move foward and be ready to support as fast as you can find in PzC.