The currency system is interesting, but it seems strange to me when you pick up money at high speed and take damage in the process. I will earn, but I will die. Yay.
The speed improvement seems to be very strong. More precisely, the progression of improvement.
I liked the new generation. Now you can walk through narrow passages, and not just through huge spaces.
I would like to see some statistics after the game: floors passed, etc.
I also found a strange bug, if this is it. When the Big charged up his attack I used my book and then he died, but continued to tremble and deal damage on touch.