Pros: the puzzle itself is pleasing to look at.
Cons: There appears to be only one layout, so it's repetitious. If you stop your game you lose it, so you can't pick up later where you left off. There are lots of ads, which wouldn't be so bad except there is no default sound setting (i.e., OFF) - so every time you open the app you get blasted with sound (I play to relax so this is a problem).
Improving these issues would go far in terms of better ratings.