What aspects of the game i need to focus?

it seems random to me if the game will be a big success or not. the tutorial don’t teach you much about every aspect of the game development. does focus on graphic belong to technic or design?
the UI is just terrible and make the game feel so random.
if someone can explain me how this work i’ll be thankfull.

Please refer to this article: http://gamedevtycoon.wikia.com/wiki/Game_Combinations