Nice simple game!
I think that this game relies too much on the randomizing of pieces, which I think becomes a problem for skilled play. Most of this game is luck at getting the correct pieces, since nothing else you have works.
It took awhile to get adjusted to how this game works, getting the "Tetris eyes" and being able to see what goes where without thinking took a bit. But, I wasn't ever really able to think multiple steps ahead quickly, and it was a slow process.
Its interesting to see how the pieces value change when you change the game like this. Line pieces become much more a hinderance then a blessing. I also found the 2x2 cube to be the most useful block.
I think the main thing to fix here, the difference between "You CANT do anything" Vs. "You could've done better" In actual Tetris, you cant never not place something, it is simply where you place it that determines who is good and who is not. Sometimes, within this you just cant do anything at all.
Despite all of this, I just kept playing it. Even though I had determined that getting a full clear was just a matter of insane luck rather than skill, I kept trying to get it for 10 minutes. I think that this shows how close this game is to being a really good, simple, addicting game (like Tetris).
Maybe a feature of rotating pieces could help with this, but I think that the actual answers to this problem may be a bit fundamental. But, nothing that a creative mind cant solve.
I really think that this is a few steps away from being a very good game.
Visuals were nice a clean. The nice animated background goes a long way to presentation.
Nice work! Excited to see if this gets expanded!