Ah, mirror Tetris!
I got the impression that this would make a pretty serious multiplayer game, if enough effort was put in to make it more fun and competitive. Stuff like scores, bonuses, and game modes would help with this.
The gameplay is very basic and straightforward (literally just Tetris), and to be honest kind of boring. I think the aforementioned features and maybe some extra speed modulation would make the game more outstanding.
Graphics and art get the job done. Nothing too special, but it doesn't really need to be.
I mean it's a little hard, because you have to manage two screens at once, but only so if you're trying to fill everything out like actual Tetris. I don't think the difficulty needs to change much, unless it's in a different game mode.
I agree with sclanim with the 3 rating... kinda average, but fun to the right audience.
Feel free to give feedback for my game as well: https://wasabiiii.itch.io/grass-elemental-demo-demo