One of the most intriguing parts of game development is balancing. How do you make a game that is neither too easy nor too hard? How do you ensure that one feature of the game isn’t so overpowering that it makes all other elements insignificant? Perhaps more importantly, who decides that? A game of any sensible size takes many months or years to develop, which means that all those working on it have an innate understanding of the interface and mechanics, so that everyone on the team finds the game too easy.
On the other hand, if you withhold the first version of the game from the testers so ...