Really nice idea and well executed. I think it would greatly benefit from having the tetris pieces come out as they do in the original game, though - that is, not completely random, since every peice will come out once before a duplicate comes out. Feel like I went way too long without getting an I block xD
Viewing post in Two games, one score (TETRIS and ARKANOID) jam comments
Even worse, tetraminos that have more permutations (like T-shaped) have more chances to appear, as we threat different positions as different shapes. So a great lesson for the next Tetris we'll do.
(You do not chace for hitting more lines in this game, though, as they'll worsen your arkanoid situation)