I've been addicted to this game for the past week or so! I like how there's an incentive to keep aiming for a higher score, as the further I go in, more mechanics seem to be added, which I find to be incredibly rewarding. I don't know if there is a manual that shows all the different pieces, but whether there is one or not doesn't impact my enjoyment at all.
A little bug I've encountered sometimes is that sometimes the option for using hints doesn't show up at all, despite having plenty in the "bank", as it were. I do not know what causes this. An addition I think would be interesting would be using the coins/money/score you've collected to "buy" an extra hint.