I think this was the first game jam I've done where I judged the scope well. Usually I try to get mechanics done on day one which I did. And when it came to content and art... Well, I did not have any! So I got to pop this one in the can quite early.
The hardest part was the level generation algorithm, making a tetris board one-step from a line that looked organic was harder than I expected. And I had to bug fix it after my first post-upload play because it generated impossible levels for the I-block!