A lot of excruciating design choices. Right off the bat, you press Z to open the menu, and then try to press Z again to open the upgrades but instead it closes the menu. It gave you no indication of what buttons do what at that point. But then it's even worse because once you only have one shot at that menu, so you have to go die to try that menu again. And you can only do one thing in that menu, so you can't save and upgrade in one go.
And of course the upgrades are way too expensive for the rate at which you gather coins. But when I finally saved 100 and tried to buy the coin upgrade, it took 100 coins from me but gave me a timer upgrade instead, which I thought cost only 60. And I didn't even want a timer upgrade.
Also, when you go to a new room by falling, there's the potential of landing on a hazard without having any time to maneuver.
And what upgrade lets you get to the coin that's walled in by those electric wire things?