Well... I played your game and it is good. I am a great fan of tetris, so I have some things to say for some improvement:
-the input in the arrow keys are too sensitive. I just couldn't play with them and had to use the mouse... I think I would have done a better score with the arrow keys =/
-I just don't understand how the score works .-. why some people have done a better score in a lower level?
-I also think you should make the speed increase faster... for me the game were boring until the level 13 and I just really feel some difference in the speed of the first level about the level 7
Well, but the game is not bad...and just one more think... you should put a limit of letters in the highscore... look how my name is there =P I can't see my score (sorry, it was also my bad =P)
The graphics and sounds were ok for me... good game, see you