Nice idea, haven't seen such mechanic. Relaxing and good looking.
I would try to lower the probability of 4 and 3 length bars as it seems like they often block the progression and you have to make meaningless move and wait for stuff to happen in the bottom. Maybe also try to be able to push the block from the bottom to the top or something like that? This is not a critique, just some ideas, I understand it's an early prototype.
I also encountered a bug when the very top row stuck after the rows to the bottom went down. And after selecting a bar from that row the game bricked (I couldn't resist the pun, sorry :))