Brings me back to the old flash game days; which is awesome!
Having some more camera action when you hit things are have gone a little bit without or are going high up would be great!
An easy way to do this is use Cinemachine since you're using Unity. It's a small thing that would greatly improve the feel of the game.
The upgrades are also nice and I like the menu art style. My only issues with the store menu is that I wish I could voluntarily pop it open with a button before I start a run instead of it popping up right after the end of one. And if the pricing was in the menu, I just clicked and hoped I had enough currency which isn't super fun. But it's a small fix since the rest of the menu is quite nice.
Other than that it does feel like the head doesn't stop fast enough; runs seem to last quite a while. Generally it's nice to keep them short especially early game, longer runs that use skill and upgrades make a great goal for progression.
It's a solid entry that with a little work would be an absolute great example of the era of flash games which stole so much of many gamers minds during school and on library computers.