Is There Any Customization In-Game?

[CTRL𝓉𝓸𝓃]

For example can you unlock block styles, change the colors of them, etc?

Thanks!

[Ferox]

You can choose between the traditional block colors or have the customized block colors chosen for the stage you're playing in. This recent update added a different block style for traditional block colors to help players with color vision deficiencies, with a nod to the gameboy tetris's way of distinguishing pieces; each piece has a different pattern.
The game's movement is fixed, this includes DAS, ARR, and soft drop speed. You can alter a few settings in local and friend multiplayer lobbies that can change some of these settings.
Outside of that, there's not much customization that doesn't involve avatars.