I keep getting A/S/Space/Down mixed up and frankly if this were mouse/touch-controlled, you wouldn't even need a separate Insert toggle, you'd just hover over where you want the piece to be. Hold could also be exclusive to the menu if it were less confusing about it too. But past all that, the game feels really nice!
The Battle Network-esque menu gauge is really cool, I love periodically planning my actions, and there's some fun risky plays like seeing a good piece coming up and avoiding opening the menu just a little longer. The lack of time pressure when actually placing pieces makes it laidback buuut does leave me wishing for more.
Also, insert is a pretty clever mechanic for how simple it is and you'd think more games would be designed around it. (Handling falling and rotating pieces tends to be pretty annoying to design & implement in my experience, especially for more exotic pieces than tetrominoes, or again, for touch screens)