Unfortunately, you're not able to play as absolutely everyone, and there's not much incentive for doing this other than witnessing more of the charming dialogue the game has to offer. (hardcoregaming101.net)
One reason is that there is not as much incentive to upgrade. (inc.com)
The biggest issue I had was that the game never really gave much incentive (outside of I suppose achievement points) to continue through. (darkstation.com)