I really like the idea, and your presentation is really good! Your game has a lot of cool juice, and especially the way the tetrominos slam into place has some really good impact.
However... in all my attempts, I either got caged early, or slipped off into a cage. The fail state is frustrating, because I have no way to recover from it(no wall jumps, it seems) - and just have to wait until I die. The game is definitely more aimed at people REALLY good at platformers, I feel. I sure can't seem to stick on a line block to save my life and always slip off D: