Just some thoughts to add on:
1) Limited crystal redemption. Limited single use items with prices that goes up too fast per item. There is never enough crystals to buy all the items required. After 6+++ runs I am always running out of crystals. Suggestion: increase crystal redemption or crystal amount.
1a) It is never worth unlocking shortcuts as the items required is limited/ too expensive.
2) Running shoes. As controls for running shoes are in the instructions, I expected to see them in the first shop or second shop I unlock instead of up to luck to get t the correct shop. Suggestion: make shoes toggleable after buying as I didn't walk after getting shoes?
3) Hats eat up limited resources and are useless. As I didn't manage to unlock the mines, if I buy the chef's hat there is no stone left to buy items and exchange for crystals.
4) Chest rewards are sometimes not worth the 80+ crystals used to buy keys.
5) Increase mining range doesn't show much increase in mining range. Mining area seems like 2 rocks touching me only.
6) Duplicate upgrades that doesn't seem to make much of a difference.
7) Unable to exchange all coupon items from the first shop. This isn't used in the other shops, which makes it awkward like why only 1 shop has it.
8) After a few runs the inventor shop barrel punching gloves are missing from purchase.
Hope this helps!