I thought that this game was great!
Very well designed in many aspects, as well as lots of balance with the upgrades. I always seemed to be completely finished with my group of upgrades right before moving onto the next set of levels. Also, the turtle's powers were cool. :)
The only issue I had with the game was how long your penguin would get stuck on the barrier. I know that's why they're there, but when I started playing I noticed I was losing because my last penguin would get stuck on some grass.
Overall a great game! 4.5 stars!
(P.S. I love penguins, that's how I found this game lol :3)