Simple but cool idea, kind of like Tetris itself. It also looks pretty polished in terms of graphics and UI.
Some other random thoughts on the game: I think it would be interesting to have the pieces appear at different locations, but that may also just be confusing. Also, I think the pieces that appear are mirrored compared to how they look in the queue, which is a bit confusing. The music is rather repetitive after a while, though the sound effects are really nice.
These are just minor things though, I really enjoyed the game :)