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I only got to the first chase scene, it proved to be so frustrating that I gave up for now.
The 'prepare for the descent' bonus challenge seems to have been implemented by offering you a choice between two types of lanterns. Well, I chose the "Distance" version of the lantern and immediately regretted it. It just doesn't work properly. Especially during the chase scene as you can't really see what's around you and thus get stuck easily.
I like the setting, that underground street is an interesting idea and the overall atmosphere is good.
The part of the game where Flint has to break into the safe in the mayor's office doesn't really make sense narratively though. Figures he could've just asked for that key and there's nothing suggesting you can do that save for a random paper on the wall that says that the key is somewhere nearby.
Overall, good job!