I find the block movement a bit fast as well. Maybe start slow and ramp up the speed over time? Also I would have liked if the first few rows were randomly prefilled with some blocks already, so you can get right into action. Really love how you implemented the scoring (building higher stacks results in more minus points, effectively preventing you from just spamming the space key) and that you added an option to end the game prematurely to preserve your score. Nice execution overall!
My game: https://njamster.itch.io/wonkey (playable in browser, not mobile friendly)