The game was genuinely enjoyable so I don't really know what feedback to give aside from "It's really fun!". the upgrades feels great to buy and use, the game doesn't try to unnecessarily pad itself out, and the game runs quite smoothly (beside when you get all the upgrade, then there's a noticeable lag where it starts from the top in one frame and immediately reach the bottom, though this is on top of 3x speed so take that as you will).
If I have any bad experience, it's mostly from my own fault, such as having clicking problem at 3x speed. As I said in my original comment, I immediately set the speed to 3x, so when it times to get rid of the debris, I essentially clicking at 1/3 the speed I could've clicked. This isn't a design problem though, I literally put the speed up myself so that's my own problem to deal with (and even then, there's an upgrade that ignores clicking later on, so it's not a permanent problem).
if you nitpick, maybe you could say the game's flow is a bit too quick? because I never once have any significant money problem, even though I forgot to upgrade most of the gold upgrades (I just bought 1 of each and forgotten about them), and I was able to quickly progress and finish the game without much issue. However, I personally prefer a game's being too quick to finish over a game being too long to finish. If you want though, you could adjust the prices more so that the game feels a bit slower without being too long, but I'll leave that decision to you, because I'd say right now it's a good flow to have.
Oh, maybe a prestige system? a common practice for these kind of games. Maybe have it appear as an option half way through the 2nd area and be like "This rock is too hard to dig through in the current era, maybe the next generation will have a technological breakthrough to dig through them?" Then you can prestige, get some kind of tech advance point, and then your digging ability is better. then again though it could be hard balancing the progression and setbacks of a prestige system, so be careful if you plan to add this (or something similar) into the game.