I've only played this single player, but the AI puts up a good challenge! The narrowing playfield is a really great idea. Despite the simple controls, I'm not sure I have a full grasp of how the pushing mechanic works yet. I look forward to trying this with a friend because I suspect there will be some fun mind games that make the gameplay a bit deeper.
One minor issue I found is that you write to palettes too soon after power-on when the PPU may still be initializing, so those writes can be ignored. (You can test this in Mesen with Settings -> Emulation -> NES -> "Clear PPU $2000/1/5/6/7 throughout first frame after reset/power-on".)