Beautiful game and an incredible concept. I have a few criticisms, but overall I found this game to be an absolute gem. I would talk more about why you should play this game, but I won't, because I think you should just go play it for yourself and see how great this game is...And also because I'm better at explaining negative feedback than I am with positive feedback. Just know that behind all the upcoming critiques, I'm actually obsessing over this game.
Now, onto the critiques...
I really wish this game had something of an ending. I love the simple endless gameplay, but after an hour-long run that shows no signs of stopping, it'd be nice to finish off by doing something like opening a third tab in the shop with one item that's worth like one million points that gives you a "the end" screen. The same stats might appear for the game over screen, but it'd give a satisfying cap on everything.
The smiley is definitely my favorite boss in the game, but I wish there was just some small change that would make revealing the boss easier when it's in a bad spot. The easiest way I found to reveal it is to find its exact tab and click on that to pull it to the top, but that's less of an option early on. I'd like it if after 20 seconds or so, the smiley would flash red and/or white all the way up onto the top layers to signal that it's about to move again, so that you don't have to wrestle with the screen any longer to reveal it from that awkward position.
Other than that, I just love this game and I wish it was so massive that it'd be unlikely to see a boss more than three times over like an hour of gameplay. I feel like if I went back in for another long run like the one I just had, I'd have pretty much the same experience, and although what I'm asking for is probably not a realistic expectation, I still felt the need to ask.