Big fan of B*p It! so I had to give this one a go.
I like what's here, and I LOVE the idea of the text getting smaller, but it's a bit too easy. I would love to see a true 'one hit kill' mode like B*p It! had...one mistake and the mode records your score for a game over. And/Or maybe a more drastic penalty for making a mistake like -10 seconds or something. I finally just stopped and let the timer run out.
Another idea would be to add in arrow symbols in addition to the up/down/right/left commands to make it even more challenging. Have the commands speed up over time and missing a command leads to a missing second?
The game could also make use of the microphone (*shout* as a command, but then you may need a 'silent' mode) or even the tilt sensor (tilt back! tilt forward! upside down!)
Just thoughts. Great idea bringing B*p it! to the Playdate!!!