I'm having a lot of fun with this game! The one problem I have (other than lag) would be: speed levels.

The fact that in Arcade Mode, speed is for lines and complexity is for squares makes it so that doing both is kind of suicide? In addition, I don't really think speed levels fit this game. I find Time Trials to be a lot of fun without them.

If you do keep speed levels, please find a different way to implement them.

Thank you for playing and giving feedback!

The thing about speed levels in Arcade Mode though is that while going up on both difficulty curves makes the game feel overwhelming, that's kind of what the game mode itself is about. It scales with how far you manages to push it, until it pushes you. And while pushing two difficulty curves at once does mean giving yourself a hard time, the game rewards you with more points if you manage to play well despite the extra hassle (in theory at least, in practice I could change the scoring system to make going for both more powerful). If still want to play Arcade Mode but don't like the speed levels though, there is always the Custom Arcade Mode where you can pick a starting speed and make it the speed for the whole run. Custom Arcade Mode doesn't save highscores though, because it would only make sense to compare highscores between identical settings and it was something I didn't think was worth the effort. Maybe later I will feel different about it though.
On the other hand, Time Trials were designed more with the idea of testing how confident you feel with the mechanics and the early piece sets. While it is closer to what you would get in a standard Tetris sprint mode, I still decided to add in the piece sets gimmick because it is more or less the defining gimmick of this game compared to regular Tetris, so I thought it made sense that the Time Trial test should be about this as well. It doesn't have the multiple pieces calling mechanic though, I feel it makes it more difficult for reasons that aren't apropriate in a sprint game.
If you want more things that don't involve speed levels though, I'm planning to have a Puzzle Mode of some sort. I still have to figure out exactly what I want to do with it (Perfect Clear a given sequence? Build a given shape? Something kind of like Tetris Plus? Something else entirely?), but it will be more about thinking how to make the chaotic shapes in this game interact together, rather than reacting to them and quick decisions.

Apologies for the late and maybe disappointing answer, but that's all I can promise.