Fairly entertaining. Only real problems here are that the difficulty goes up exponentially, too fast after level 5 for you to keep doing next levels (means you're forced to farm coins at around level 6, and I'd prefer not to have to) and that I got all the medals while logged out of NG, but can't get them now that I logged in (might want an NG metal check either as a button on the medals screen or have one run when the medals screen opens). I might play again in a different browser in case a metal check doesn't get put in though.
Another thing, though it may not be extra major, is that you'd need to have a 600-700 clicks per minute clicking finger (unassisted by auto-clickers) like mine to be able to beat the later levels in time, especially if you don't upgrade strength almost every time until it's maxed. Even then, with max strength, having to focus exclusively on mashing Z and X with both index fingers forcing you not to be able to move isn't much fun on the last 2 levels. I like difficulty, but I prefer keeping my mouse hand on my mouse and my keyboard hand on my keyboard.
One more issue is that how fast rocks can fall is crazy, especially with the need for vertical speed. Maybe having a Perception upgrade to allow you to see pickups and falling rocks more easily (perhaps by zooming out and/or moving the character lower on the screen so you see further above yourself) would be a nice addition.
Finally, to satisfy the guys complaining about the controls, you can switch it to Left Arrow and Right Arrow and say "Alternate between those two keys" so people think "Left then Right" instead of "left and right at the same time."
Other than all that, this was a fun way to spend about a half hour.