Where do I even start?
Like Submachine or Arcane before it, this is a perfect point & click adventure/puzzle game. Other games wish that they had the scope and fun of this series. The walkthrough is handy, but unlike some games, not necessary for much of the game. I didn't even need it until I got to the library, but much of it was instinctual. I love the use of actual German in this, as so often, German as a culture & language is disrespected or stereotyped.
That aside, the plot is phenomenal, and really gives the feel of a spy thriller! I love that it's set prior to the Great War, because that sets it apart from all the games set in the cold war or world war II, or even post cold-war. There are hardly any decent thrillers with exciting stories like this, and playing the part of the spy makes it so much cooler than any other game I've seen on NG. I cannot wait for part 4!