I haven't had any real issues with the switch to UE4, though I just started a few days ago and don't know the difference between that and the original. However, I did experience a few bugs when it came to using the overview map in chapter 3, where I had to click a few times occasionally to get it to register.
That said, I really enjoy this. There is another text based game I love called Parasite Infection which is pretty similar, except in an old thread on another site I saw people talking about older versions of the game sticking to Earth, having you gradually take over more and more. I liked that idea and, while I still love Parasite Infection, at the time kind of wanted something like what I saw described.
You made and are still making that something, and I greatly appreciate that. Keep up the good work. I love the idea of being able to gradually take over the world a city at a time. I also hope a save feature is implemented, until then I love just skipping to chapter 3 and playing around seeing what I can do with the nearby cities.