I loved Threediopolis. It's inventive, I got a kick out of seeing all the interesting places I could go, and the difficulty was challenging yet fair. When I heard there was a sequel, I couldn't wait to jump in and see what kind of new mechanics were added.
Figuring out Fourdiopolis for the first time gave me much the same experience as Three. I tested my moves, tracked what they did, then found the letters I needed to use to get somewhere close. I (Spoiler - click to show)met Ike first, and after that, everything clicked.
I think I had a harder time finishing Three; not only because that game had more tasks before the first "ending" point, but the number jumping felt a bit more severe. Also, in Four, your completed tasks are listed in alphabetical order. This was a big help, since for every destination I chose, I had a good idea of which letters it could start with.
I love the different vibe of Four. Three had you traveling around a city to complete tasks for your employer. Meanwhile, this game's atmosphere is futuristic and throws you into a controlling society where you're witnessing rebellions and captures. Everything feels more oppressive and hostile. It's a big change of tone, but it sets the games apart pretty well.
I was kind of relieved Four ended when it did; while I was open to (Spoiler - click to show)completing 15 more tasks, I didn't want to do it immediately afterwards, having just solved similar puzzles for an hour straight. I might pick this one up again in the future to see if I can make it further, but now I really feel like replaying Three. If you liked the predecessor, check this one out. Otherwise, you should probably play Three first.