He warns that the preferred piece is an S in the docs. But I was able to force the game to generate squares and lines with "good" play. (I could predict by the end which piece it would pick with reasonable accuracy.) To do better (at least based on my watching the high score replays), you have to intentionally "play badly" and make gaps that open up if you clear a middle row of the gap. The 17-replay I saw generated tons of lines, which I honestly wouldn't expect this app to generate.
