As other people have said, a hold function and being able to hold the left/right arrows to quickly move left/right would be awesome.
Besides those two nitpicks, this is a very, very unique take on Tetris, and it's really unfortunate that the Tetris Company is as sue-happy as they are, because I'd love to see this turned into a multiplayer online game. Incredibly fun and challenging, this is seriously an awesome idea.