Thanks for your comment! You also should know that there are cool sound effects that you can't hear very well on the video. And yes, design of apps is one of my weak points. I really don't know what to do to create a great design. When I try something with colors the interface starts to look very cheap and unprofessional, that's the reason why I keep it very basic. Does anyone has some tips to learn designing apps? That should be great!
I personally think that your app is quite cool since the amount of interactivity compensates for the design. I like how the presence of the minigames spices up the experience. So yeah, the lack of a supposedly "good" design doesn't really deteriorate the experience. On top of that, good design comes with experience. I remember how bad my designs were when I started programming 3 years ago, but I definitely improved in the past years (especially when iOS 7 came out).