Whole idea of playing on the finger was actually amazing! It was satisfying cute little game. I enjoyed it.
The only thing I would suggest is making walls disappear after some time (or last wall disappears if you put one more than you can). Because when you run and build it is sometimes a bit inconvenient to move mouse back and try to find walls to erase to get few additional blocks. That would also restrict player from just building walls and farming exp (although not sure about that since i liked to block myself and just farm for a bit :D) But these are just a small things.
Overall, It was great game, felt polished and I am looking forward for more content if the future!