Not to shabby!
Really, this is a nice game!
I only got two objections:
1.) Unlike Tetris, the "active" fiel is moving - this causes misclicks if u try to move blocks just in the moment when a new row comes
2.) At times, there are simply not enough blocks, and you got to wait until there are new rows.
Possible solution for 1.): Make the blocks move up at a constant speed. If you do not wish blocks which would be - at this rate - half visible, make them plain black and dont allow to move them.
Possible solution for 2.) Maybe add 3 more rows, and set a minimum of 3 rows which will instantly refill when cleared. This way the player will always have blocks to play with.