I just got The Moon Is Our Friend and I think it's a perfect Playdate game, at least for the kind of games I like to play on it (I don't care much for the more RPG/story-driven stuff). It's addicting, and it uses the crank in a way that makes the crank feel indispensable.
I also discovered the Mirror app and it turns out it's a big deal for me! I love the form factor of the device and I'm fine with a black and white concept, but the combination of screen size and the lack of a backlight does take some enjoyment out of it all that Mirror gave back.