I pretty much agree with DaggerPen's points; this is an awesome game. First off, the music is very nice and dynamic, which is always welcome. Secondly, the graphics are sweet, neat, and also smooth. Third, the controls are simple and easy to use. Fourth and last, features are easily accessible; there is no need for a lot of awkward menu navigation when dealing with stuff like the types of creatures that have been discovered. This also ties in to the simplicity of the gameplay, which is okay.
There are some gripes, though. The story is a bit... simple, especially when the end is taken into account. However, considering the cheery nature of the game, I suppose that does not hurt it too much. Additionally, the arrows, once you reach the deep waters, are not as visible as those in the normal waters; this especially applies to the confrontation with the kraken. Furthermore, the kraken itself felt weak; maybe it's because I got the best fishing pole, but when I tried reeling in the kraken. For one thing, it was surprisingly easy to complete... heck, it was easier to catch than the whales. It should have been a bit tougher to reel in, because that felt somewhat anticlimactic. As well, like I said before, the arrows were not entirely visible since they blended in with the darker colours.
Of course, there can always be more features. Firstly, there could have been more areas to explore, with other fish/sea mammals. Secondly, medals would work well. For example, referring to DaggerPen's suggestion, you could have a medal for obtaining the maximum number of whales in your boat (though it probably should be the Hemmingway Ultra Yacht) called "Whale Done" or something to that effect (it doesn't have to be a cringe-worthy pun, though). Lastly, piggybacking on the first suggestion, there could be some unique "mini-boss" creatures, such as a mermaid, like zarfas suggested.
Well, I'm done with my rant. Overall, it's a good game. It could use a bit more polishing, but it's not mandatory for getting fun and enjoyment out of this.