Loved the game. Some observations:
* Newly upgraded tools felt like they moved slower than the older tools. Even if they harvested more in the same amount of time. Difference was barely noticeable. In a way, the slower movement gave the new tool more weight and mass, which could be what you wanted. Even so, giving the new tool maybe 30% more harvesting ability would be more noticeable, and give more of a sense of 'woah!' Also more true to real life.
* Enjoyed the ground floor forest level. Second level was a bit of a grind. Third level desert I got fed up of the grind and ended up cheating (?) most of both the third & 4th levels through being able to almost fill then take back my resources in the two shops. Each time I take back, I get about 20% more than I gave. Which was a better use of time than grinding. Eg give 100 leather, get back 120 leather, give 120 leather, get back 150 leather .... give 600 leather get 750 back etc. Was able to get all 3 tool upgrades and most of the black market stuff in a few minutes like this. More enjoyable than grinding bags of rubbish. I do suggest you think of reducing the grind for 3rd level onwards or giving alternate ways of getting large amounts.
* Third level desert - I was exploring it in the dark and fell through the world at the edge of the map. Seems a boundary error. Couldn't make it happen in the light, but seems I can travel through all outer boundaries when in the dark. Almost certainly a bug, but it does seem you could make this part of the horror theme if you wanted.
* 5 level flesh (incomplete) - I was able to jump on top of the furnace and from there jump to the top of the lighthouse. Don't know if this is intended but it was fun. Another comment mentioned a 10,000 furnace up there, but I didn't see any sign of it. Has it gone? Entering the top of the lighthouse results in being thrown to the edge of the map. Quite fun, and something you could do more with.
Hope this feedback has been helpful!